Gynoecium and Fruit Histology and Development in Eugeissona (Calamoideae: Arecaceae)

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Botanical Journal of the Linnean Society, 2012, 168, 377–394. With 6 ﬁgures

Gynoecium and fruit histology and development in Eugeissona (Calamoideae: Arecaceae)

ALEXEY V. F. Ch. BOBROV1*, JOHN DRANSFIELD2 FLS, MIKHAIL S. ROMANOV3 and 4 EKATERINA S. ROMANOVA Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021

1Department of Biogeography, Geographical Faculty, M. V. Lomonosov Moscow State University, Moscow, 119991, Russia 2Herbarium, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK 3Department of Dendrology, Main Botanical Garden nm. Tsitsin N. V. RAS, Botanicheskaya st., 4, 127276, Moscow, Russia 4Botanical garden, Biological Faculty, M. V. Lomonosov Moscow State University, Moscow, 119991, Russia

Received 14 June 2011; revised 18 August 2011; accepted for publication 6 December 2011

The Malesian genus Eugeissona, with six species, is sister to all other Calamoideae, which are in turn sister to all other Arecaceae. The structure of its gynoecium and fruit is thus potentially of great interest in understanding gynoecium evolution in calamoid palms and in Arecaceae as a whole. The wall of the incompletely trilocular gynoecium of Eugeissona is thick and differentiated into several topographic zones, with a well-developed vascular system even before pollination. During gynoecium and fruit development, the outer and inner epidermises are little specialized and form the exocarp and endocarp (obliterated in the mature fruit), respectively. In contrast, the mesophyll of the carpels differentiates strongly and is markedly specialized: four massive topographic zones are easily distinguished within the mesocarp. The peripheral zone of the mesocarp forms the body of the scales (a synapomorphy for Calamoideae). The second and the fourth zones are multilayered and parenchymatous with a massive derived vascular system in the former. The third zone of the mesocarp comprises a stout sclerenchymatous pyrene, made of ﬁbre-like sclereids, the innermost bundles of the derived vascular system and dorsal, ventral and lateral vascular bundles. The fruits of all other Calamoideae lack the sclerenchymatous pyrene and thus differ dramatically from Eugeissona fruits. The similarity of the processes of histogenesis during gynoecium and fruit development in Eugeissona with those in Nypa and borassoid palms, suggests these features could be plesiomorphic for the family. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 377–394.

ADDITIONAL KEYWORDS: Borasseae – carpel wall structure – Nypa – pericarp anatomy – pyrene – scales – vasculature.

INTRODUCTION Eugeissona is thus of great importance for developing perspectives of gynoecium and fruit development in The genus Eugeissona Griff. has recently been shown the family. The gynoecium of Eugeissona (and all to be sister to all other Calamoideae, which are in genera of Calamoideae) is termed ‘incompletely turn sister to all other Arecaceae (Asmussen et al., trilocular’ (Dransfield & Uhl, 1998; Dransfield et al., 2006; Dransfield et al., 2008; Baker et al., 2009). An 2008). Nevertheless, the fruits of Eugeissona differ investigation of gynoecium and fruit development of from those in other genera of Calamoideae in the development of a thick sclerenchymatous pyrene in the pericarp. The dramatic difference in the general structure *Corresponding author. E-mail: [email protected] of the fruit of Eugeissona from other taxa of

Calamoideae was recognized by Beccari (1913), highly specialized fruits: both apocarpous (Schippia Corner (1966) and Dransfield (1970); Beccari sup- concolor Burret) and syncarpous (Chuniophoenix posed that the fruit of Eugeissona is the ‘connecting Burret, Kerriodoxa elegans J.Dransf., Sabal Adans.) link’ between the fruits of Calamoideae and monospermous berries (Bobrov et al., 2008b). A much Arecoideae tribe Cocoseae, which also have a thick more complex structure of the pericarp (and the pecu- sclerenchymatous pyrene. Nevertheless, the histoge- liar mode of the pyrene development) is described for nesis of the pyrene in Eugeissona has not been syncarpous fruits of Coryphoideae tribe Borasseae described in the literature. Recent data support the (Romanov et al., 2011), which are referred to pyre- isolated position of Eugeissona among Calamoideae, naria of the Latania type. In contrast, fruits of most which is also supported by other morphological char- species of Calamus L. are monospermous (a few are acters (Dransfield et al., 2008); for example, the dispermous or trispermous) paracarpous berries Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 branching by putative dichotomy of the apical mer- covered with gynoecial scales, making the structure istem (Fisher, Goh & Rao, 2008), partial centrifugal of the fruits more complex (Bobrov, Romanov & stamen development (Uhl & Dransfield, 1984) and by Melikian, 2011). Thus, the problem of what consti- unique nectar with high concentrations of alcohol, tutes the plesiomorphic and what the derived state in securing pollination by small arboreal mammals (slow the structure of the pericarp of Arecaceae remains loris, pentailed tupaias, etc.) (Wiens et al., 2008). unsolved, and an investigation of gynoecium and fruit Since the time of Drude (1887), palms with apoc- structure in Eugeissona will contribute to an analysis arpous gynoecia have tended to be treated in tradi- of which characters should be treated as plesiomor- tional classifications as the most archaic (Hutchinson, phic for Calamoideae and palms in general. 1973; Moore, 1973; Imkhanitzkaya, 1985; Takhtajan, 1987). In the first edition of Genera Palmarum (Uhl & Dransfield, 1987), Coryphoideae was considered to be MATERIAL AND METHODS the least specialized subfamily, and the presumed Material of Eugeissona species fixed in formalin– most archaic taxa of the subfamily were genera with acetic acid–alcohol (FAA) and dry herbarium speci- apocarpous gynoecia in Corypheae subtribe Thrinaci- mens were used in the present study (see Table 1). nae (Dransfield & Uhl, 1998). The interpretation of Morphometric information for all studied develop- apocarpous palms as primitive agreed with the gen- mental stages is given in Table 2. Standard anatomi- erally accepted evolutionary concept of gynoecium cal protocol was used for anatomical investigations types, according to which the apocarpous gynoecium (Bondartzev, 1954; Prozina, 1960; O’Brien & McCully, is the least specialized and the coenocarpous (i.e. 1981). The liquid-fixed gynoecia were embedded in syncarpous, paracarpous and lysicarpous) derived wax and transverse (TS) and longitudinal sections (Bessey, 1915; Takhtajan, 1964; Hutchinson, 1973). (LS) at 9–15 mm were made with a Jung rotary micro- Recent DNA sequence data have shown that Calam- tome. These sections were stained with safranin and oideae, all representatives of which have paracarpous fast green, and TS and LS (15–30 mm) of developmen- gynoecia, are sister to the rest of Arecaceae (Asmus- tal stages of Eugeissona fruits were carried out with sen et al., 2006; Dransfield et al., 2008; Baker et al., a sliding microtome from the samples embedded in 2009), with the possible implication that the gyno- paraffin. These sections were stained with phloroglu- ecium with free carpels found in some Coryphoideae cinol and hydrochloric acid to study details of lignifi- and Nypa Steck should be treated as secondarily cation of cell walls in different topographical zones of apocarpous, reopening the question of which type of the pericarp and were preserved in glycerine. All gynoecium is plesiomorphic in the palms. sections were studied with a light microscope. The The structure of apocarpous fruits of the investi- details of gynoecial scale development (= pericarp gated representatives of Coryphoideae is rather spe- surface) and of fruit-wall structure were also exam- cialized and cannot be treated as plesiomorphic ined with scanning electron microscopy (Camscan (Bobrov, Romanov & Romanova, 2008b). The mode of S-2), after critical-point drying and sputter coating development and structure of the stone of ‘coryphoid’ with gold palladium. fruits, described by Murray (1973) for Rhapidophyl- lum hystrix H.Wendl., Livistona R.Br., Pritchardia Seem. & H.Wendl., and Washingtonia H.Wendel. and TERMINOLOGY studied by us in Trachycarpus H.Wendel., Chamae- At all developmental stages, three histogenetic zones rops humilis L., Rhapis L.f and Guihaia J.Dransf., of the pericarp derived from the outer epidermis, S.K.Lee & F.N.Wei (Bobrov, Džalilova & Melikian, mesophyll and inner epidermis of the ovary wall were 2007a; Bobrov & Romanov, 2007; Bobrov, Romanov & recognized: exocarp, mesocarp and endocarp. The rec- Melikian, 2008a) is treated as specialized. Moreover, ognition of these zones as histogenetic, but not topo- a number of representatives of Coryphoideae have graphic, is important for developmental studies

Table 1. Investigated species and specimens

Eugeissona insignis, J. Dransfield no. JD747, 27.3.68, Bako National Park, Sarawak, alt. 10 m, in kerangas forest, RBG Kew Palm group collection and BH spirit collection, gynoecium stage 4 Eugeissona insignis, J. Dransfield no. JD754, 29.3.68, Bako National Park, Sarawak, alt. 10 m, in kerangas forest, K, fruit stage 4 Eugeissona insignis, Moore no. 9105, BH spirit collection, fruit stage 4 Eugeissona minor, J. Dransfield no. JD777, 10.04.1968, at Bukit Urang, Bintulu, Sarawak, East Malaysia at 30 m alt in kerangas forest, BH spirit collection, gynoecium stages 1, 2, fruit stages 2, 3 Eugeissona minor J. Dransfield no. JD803, 23.4.86, mile 7, Andulau Forest Reserve, Brunei, alt. 70 m, lowland

dipterocarp forest, BH spirit collection, fruit stages 2, 3, 4 Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 Eugeissona tristis, J. Dransfield no. JD816, 11.5.68, Kluang Forest Reserve, Johor, Peninsular Malaysia, 30 m alt., swamp margin, BH spirit collection, fruit stage 4 Eugeissona tristis, Moore no. 9059, BH spirit collection, gynoecium stage 4, fruit stage 4 Eugeissona utilis, J. Dransfield no. JD797, 20.4.68, mile 10, Muara Road, Brunei, alt 30 m, secondary forest, BH spirit collection, fruit stages 1, 3, 4 Eugeissona utilis, J. Dransfield no. JD804, 24.4.68, mile 7, Muara Road, Brunei, alt 30 m, secondary forest, RBG Kew Palm group collection and BH spirit collection, gynoecium stage 3 Eugeissona utilis, Moore no. 9219, BH spirit collection, fruit stage 2

(Cave, 1869; Garcin, 1890; Bobrov, Melikian & species is not significantly different, apart from the Romanov, 2009). At the same time, exocarp, mesocarp development of additional ridges in E. insignis and endocarp are often recognized as topographic described below. They differ in size and the available zones and, in this case, the term endocarp is applied material makes up a continuous developmental to different histogenetic zones of the pericarp made of series. The first three stages represent the gynoecium sclerenchymatous tissues, developing from different removed from the flower before anthesis and the zones of mesophyll or from the locular epidermis of fourth stage is the gynoecium after anthesis. At this the gynoecium. A detailed classification of endocarps last stage, all three ovules still continue their growth made up of sclerenchymatous tissue was proposed by and development (differing from the first stage of fruit Roth (1977), representing a histogenetic classification development studied, when only one or two of three of stones and pyrenes of apocarpous and coenocarpous ovules continue their further growth). drupaceous fruits, respectively. To avoid confusion in terminology, we propose to use the term ‘endocarp’ in Eugeissona minor a histogenetic sense only. We propose to use the term At the first (earliest available) stage of development ‘stone’ for apocarpous fruit(let)s and the term ‘pyrene’ (see Table 2), the trimerous symplicate ovary of the for coenocarpous (i.e. syncarpous, paracarpous and gynoecium is hemiovoid (c. 3 mm high) and topped lysicarpous) fruits, for the description of the inner or with a pyramidal triangular style, symplicate in the middle sclerenchymatous zone of pericarp. Epicarp, basal part and plicate in the distal part, c. 1.3 mm which in some cases is treated as a synonym of high with three glandular slits descending from the exocarp, as used in Dransfield et al. (2008), is pro- tip of the style to its base (Fig. 1). Originally the posed to be treated as the extracarpelar zone of the gynoecium is bare (Fig. 1) – the surface is covered fruit wall that develops from any extracarpelar part with regular vertical rows of epidermal cells (Fig. 2). of the flower. The term ‘epicarp’ is better applied to The differentiation of gynoecial scales has not yet the fruit wall of inferior (or the lower part of semi- begun. At the second developmental stage, the origin inferior) fruit, but not for superior fruits (as are all of the scales on the gynoecium surface becomes palm fruits). Epicarp is usually differentiated into apparent when the gynoecium is approximately epidermal tissue and main tissue. 4–5 mm high and topped with the trimerous pyramidal style (c. 2 mm high) composed of three tightly adpressed lobes with stigmatic contacting surfaces RESULTS (Fig. 3). The scales develop basipetally in vertical THE GYNOECIUM rows; the original regularity is interrupted in the The development of the gynoecium was studied at proximal part of the gynoecium because of the inter- four arbitrary developmental stages available for polation of new rows (Fig. 4). Scales develop as hemi- Eugeissona minor Becc., E. utilis Becc., and E. insig- spherical protuberances on the gynoecium surface nis Becc. (see Table 2). Gynoecium structure in these and are composed of an outer epidermal layer and

several layers of parenchymatous cells in the peripheral zone of the mesophyll (Figs 4, 6, 31 and 33). 5.1 4.0 5.0 5.0 ¥ ¥ ¥ ¥ Later the scales become peltate with broader ﬂat- tened distal parts partly covered with hairs (Figs 6 and 33).

Eugeissona utilis In the third gynoecium developmental stage, shortly 4.5 8.3 4.0 6.5 ¥ ¥

diameter in cm before anthesis, the major portion of the gynoecium is

¥ the nearly cylindrical symplicate ovary, which is partly widened distally and then sharpened into a Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 short basally symplicate and distally plicate pyramidal triangular style with three tightly addressed stigmatic surfaces (Figs 5, 9). The symplicate zone of the 3.2 6.8 3.2 6.0 ¥ ¥ style transforms into the plicate zone at its middle level (cf. Figs 2, 23, 24). The distal broad part of the gynoecium is covered with fully developed scales, whereas proximally new scales still arise in a basipetal direction. The single locule is located in the central part of the 1.8 5.0

¥ gynoecium; it is displaced somewhat to the proximal

1234 part. This locule originates as the result of incomplete closure of three original locules of three carpels fusing by their margins and contains three ovules (one per each original locule). The three ‘original’ locules are interconnected at different levels of the ovary in 0.9 – – – 8.3 0.8 – –transverse section. – In the distal 9.2 part of the ovary, the ¥ ¥

species locule gradually tapers and continues through the style as a triradial slit (Figs 19–22); distally it becomes triangular in transverse section (Fig. 23). At this level (and above, up to the top of the gynoecium) the differentiation of three glandular slits is observed Eugeissona

diameter in cm Fruit developmental stages, height on the surface of the style (Fig. 23). A little more 0.38 – 3.0 ¥

¥ distally the stigmas become separated and so the triangular apical slit of the locule connects to the outside (Fig. 24) and ﬁnally separates into three stigmatic lobes (Fig. 25). Inside the locule, at its base, the central protrusion of the inner ﬂoral base can be observed (Figs 13–15) with three basally attached anatropous bitegmic crassinucellate ovules. The

0.33 –central – protrusion –of the inner ﬂoral 5.0 base has a more ¥ or less triangular outline in cross section and it continues nearly up to the central part of the ovary locule. Three longitudinal ridges, which are the fused margins of three adjacent carpels (as indicated by two ventral bundles in each invagination) also deeply penetrate into the locule (Figs 14–18, 26–28). The

0.28 0.47 initiation of invaginations in the locule corresponding ¥ to the dorsal vascular bundles is just beginning at this stage of gynoecium development (Fig. 17). – – 0.60 Gynoecium developmental stages, ovary height –––2.3 1234 0.30 –––1.7 The ovary wall is made up of an outer epidermis, multilayered mesophyll and inner epidermis. These The studied gynoecium and fruit developmental stages of zones will ﬁnally be transformed into exocarp, mesocarp and endocarp, respectively. The mesophyll is differentiated into four well-deﬁned zones, which E. utilis Table 2. E. tristis E. minor E. insignis markedly differ at different levels of transverse

© 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 377–394 GYNOECIUM AND FRUIT DEVELOPMENT IN EUGEISSONA 381 sections: from the proximal part of the ovary (below 17, 27). In this way, they form three isolated longitu- the locule level) (Fig. 12) up to the locule distal end dinally elongate cavities inside the fused ventral level (Fig. 19). At the very base (Fig. 12), the gyno- bundles in the three largest inner gynoecial ridges. ecium is made up of thin-walled unspecialized paren- The gynoecium is vascularized by numerous vascu- chymatous cells (except for the epidermis) differing lar bundles (Figs 10, 11). At the flower base there are from each other by size, shape and content (indicated peripheral circles of vascular bundles supplying the by different colouring). corolla and inner vascular bundles of the gynoecium, The differentiation of the carpel wall is similar at they in turn supplying the inner zone of the gyno- all levels of the gynoecium locule, from its base to the ecium and ovules. The vascular system of the gyno- top (Figs 13–18, 26–29). ecium is made up of three complexes of the bundles The outer epidermis is made up of small isodia- for each carpel. It is represented by the main vascular Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 metric or partly radially elongated cells with regu- bundles entering the carpel independently and the larly and scarcely thickened primary walls (Figs derivative vascular bundles. The main vascular 26–29, 31–33). Epidermal cells participate in the bundles are represented by one dorsal, one or two formation of the scales; they cover them on all sides. pairs of main lateral and two ventral bundles bifur- The mesophyll is differentiated into four topographic cating from the main ventral bundle and also giving zones (Figs 26–29). The outer topographic zone con- rise to the funicular bundle, providing the vascula- sists of five to seven cell layers that (with single- ture of the ovule. The numerous small derivative layered outer epidermis) participate in the formation (proto)vascular bundles in the peripheral (the second) of the gynoecial scales (Figs 31–33); the cells becoming zone of the mesophyll arise from the main lateral larger in the direction of the base of the scales. bundles. There is a stout vascular bundle of The second, the peripheral zone of the mesophyll, is the central protrusion of the inner floral base in the parenchymatous and has a dense network of deriva- centre of this section. This bundle originates as the tive protovascular bundles (Figs 26–29, 31–33). This result of the joining of three vascular bundles arising zone is made up of 19–25 layers of polygonal colour- from the basal ventral bundle entering each carpel. less cells and scattered among them cells containing The funicular vascular bundles of the ovules (three in tannins. The protovascular bundles numerous in this total) and dorsal vascular bundles of each carpel zone and differ in size. They derive from the vascular (three in total) lie on the same radial lines. bundles of the gynoecium and are distributed in several concentric irregular circles. The third topographic zone has a complex outline Eugeissona insignis (circular with inner ridges) and primarily consists of a At the fourth developmental stage, the ellipsoidal protovascular system: the circular part is made up of ovary contains three well-developed ovules filling the numerous longitudinal protovascular bundles and the locule. The anatomy of the ovary wall does not show ridges correspond to the primary (main, skeletal) vas- dramatic changes when compared with the earlier cular bundles. The longitudinal protovascular bundles stages (E. utilis), illustrating the third gynoecium are regularly distributed and separated from each developmental stage: the general topography of the other (and covered from other sides) by parenchyma- gynoecium wall remains unchanged and the number tous cells with thin walls and granulated cytoplasm. of cell layers of most zones of mesophyll increases a The third topographic zone is made up of 12–15 layers little. The scales are fully developed and cover almost of small isodiametric cells, which become somewhat the entire gynoecium, overlapping with each other in tangentially elongated towards the inside. four or five layers (Figs 34, 35); scales at an early The fourth, innermost zone of mesophyll is made up developmental stage can be observed only at the very of (6–) 10–12 layers of rather polygonal or partly base of the gynoecium, which is covered by the peri- tangentially elongated thin-walled parenchymatous anth (not shown). At this (the fourth) stage of gyno- cells. The inner (locular) epidermis of the carpel is ecium development, the derivative vascular bundles made up of isodiametric cells covered with a thin are better differentiated and their sheaths begin to cuticle. develop around them. Differing from all other Eugeis- The ventral vascular bundles of the carpels are sona spp. studied (see Table 2) in E. insignis, three covered on the inside with the fourth zone of the additional pairs of stout lateral vascular bundles mesophyll and the locular epidermis and form develop inside from, but not within, the third zone of the longitudinal ridges, which deeply penetrate into the mesophyll; they develop on both sides from the the locule and represent the fused margins of the dorsal vascular bundles in each carpel comprising the adjacent carpels. At the level of the middle of the gynoecium (Figs 34, 35). Finally they develop into carpel locule, these invaginated carpel margins do not six additional internal ridges in the mature fruit fuse in the middle part (in radial direction; Figs 15– (Figs 43, 44).

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THE FRUIT stages are sequential but were determined by the Eugeissona utilis stages present in the material available (see Tables 1 and 2). At the ﬁrst stage, the fruit is obovoid with a Anatomical structure of the fruit was studied at four terminal conical stigma from which the scales had arbitrary developmental stages described below developed basipetally (Fig. 36). The distal part of the under the numbers 1–4 (Figs 36–41, 45–52). The fruit is covered with well-developed scales, but the

Figures 1–8. Scanning electron microscopy (SEM) images of developing gynoecium and transverse sections (TS) of pericarp hardy zone. Figures 1–4. Eugeissona minor. Fig. 1. Upper view of the hemiovoid gynoecium covered with epidermis (scales are not developed yet) at the early (first) stage of development. Fig. 2. Close-up of gynoecium outer epidermis surface from Fig. 1 showing the regular vertical rows of epidermal cells, upper view. Fig. 3. Lateral view of the gynoecium at the second developmental stage topped with a trimerous pyramidal style and partly covered with scales developing from the base of the style downwards. Fig. 4. Close-up of gynoecium scales developing in interrupted vertical rows, lateral view. Figures 5–8. Eugeissona utilis. Fig. 5. Lateral view of the third developmental stage of gynoecium half covered with basipetally developing scales. Fig. 6. Close-up of gynoecium scales developing in irregular vertical rows, lateral view. Fig. 7. Transverse section of the third zone of the mesocarp (the pyrene) of the mature fruit (stage 4), note the orientation of cells in different directions; the bottom edge of the figure shows the fourth zone of mesocarp. Fig. 8. Close-up of TS showing fibre-like sclereids with heavily thickened walls, note the orientation of cells Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 in longitudinal, tangential and oblique directions. (Scale bars,1 mm (Figs 1, 3, 5); 0.1 mm (Figs 2, 8); 0.5 mm (Figs 4, 6, 7). ᭣ basal part, surrounded by the flower parts, is still developing. The thickness of this circular zone is covered with scale primordia, similar to those 40–50 layers of cells. The ridges correspond to the covering the gynoecium at early developmental primary (three dorsal and three ventral pairs) vascu- stages – the second and third stages of gynoecium lar bundles (Figs 37, 47). They are united with the development (Figs 3–6, 31–32). The pericarp is com- circular zone by the interlacing nets of fibre-like cells posed of 245–260 cell layers (Figs 45–48). The exocarp oriented in a longitudinal or radial direction (identical covers the scales and the space between them and is with those comprising the circular part of the third represented by somewhat isodiametric epidermal zone of the mesocarp). The pairs of ventral bundles cells with thickened walls (Fig. 46). The cells covering (corresponding to two neighbouring fused carpels) are the scales possess tannins in the lumens and have Y-shaped in transverse section (Figs 37, 47). Three heavily lignified walls. The mesocarp is differentiated ovules are observed in the locule at this stage, two into four topographic zones clearly corresponding to small, degenerating ones and one larger, which will the four zones of the mesophyll revealed at the third finally develop into the seed (Fig. 37). and fourth stages of the gynoecium development The fourth zone of mesocarp is made of up to 100 described above. The outer zone of the mesocarp layers of isodiametric parenchymatous cells with pale comprises the body of every scale and is represented contents and thin walls. There are regular rows of the by five to seven layers of isodiametric sclereids with multiplying cells in the innermost part of this zone thickened lignified walls. This zone develops only in (Figs 47–48). the scales and is interrupted between them. Next, the The endocarp is represented by an undulating second zone is made up of approximately 100 layers of locular undifferentiated epidermis made up of thin- parenchymatous cells with numerous vascular walled isodiametric cells covered with a thick cuticle bundles arranged in irregular concentric circles. The (Fig. 48). The cells continue multiplication in a tan- parenchymatous cells are more or less idodiametric gential direction. but differ in size. The vascular bundles are more At the second stage of development, the fruit is still numerous in the peripheral zone of the mesocarp; obovoid and c. 3.2 cm in diameter (Fig. 38, Table 2). they have stout sheaths (made up of cells with thick- The structure of the pericarp shows some differences ened and partly lignified walls) on their abaxial faces. in comparison with the previous stage (Fig. 49). The The parenchymatous cells around them are smaller. gynoecial scales are finally differentiated at the basal The third zone has a complex structure; it is repre- part of the fruit. The cells of the second zone of the sented by a circular part connected with six internal mesocarp become somewhat tangentially elongated longitudinal ridges (Figs 37, 47). The zone is made up and rather numerous tannin-containing cells become of regularly developed longitudinal vascular bundles conspicuous, either solitary or in groups of several (Fig. 45) (corresponding to the protovascular bundles (Fig. 49). As a result of the lateral growth of the described in this zone in the gynoecium; Figs 26–29) pericarp (enlargement of the fruit diameter), the surrounded by developing abaxial stout sheaths. number of layers of this zone decreases to approxi- These vascular bundles with massive sheaths are mately 75. The walls of the cells comprising the united with each other by numerous fibre-like cells massive sheaths of the vascular bundles become with thickened walls. They are oriented in different thicker and lignify. The walls of the cells comprising (longitudinal, tangential and oblique) directions and the third topographic zone of the mesocarp become form a network. Inside the bundles c. 20 layers of thicker at this stage and their lignification begins. At primarily tangentially elongated fibre-like cells are the second stage, the largest ovule fills the whole

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Figures 9–18. Eugeissona utilis, microtome longitudinal sections (LS) and transverse sections (TS) of the third stage of gynoecium development. Fig. 9. LS through the central zone of the mature gynoecium before pollination, horizontal lines indicate the levels of TS of the same gynoecium illustrated on the further figures with numbers corresponding to the numbers on the right. Fig. 10. TS through the base of the flower showing the disposition of vascular bundles: peripheral circle (arrow) supplying the corolla and inner vascular bundles of the gynoecium itself (located inside the peripheral circle of the vascular bundles). Fig. 11. TS through the base of the flower, note the peripheral vascular bundles (of the corolla), inner (the gynoecium) bundles making the central triangular zone (within asterisks) and three large dorsal vascular bundles (arrow) corresponding to three locules of the gynoecium. Fig. 12. TS of the gynoecium below the locule level, note the differentiation of the peripheral zone and middle zone of gynoecium wall. Fig. 13. TS of the gynoecium through the locule base, note the differentiation of the gynoecium wall, the base of the central protrusion of the inner floral base

(asterisk) partly with the margins of three adjacent carpels (arrows). Fig. 14. TS of the gynoecium with central protrusion Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 of the inner floral base with three basally attached placentae (arrow) and fused margins of three adjacent carpels (asterisks). Fig. 15. TS of the gynoecium, note the distal part of the central protrusion of the inner floral base in the centre, the fused margins of three adjacent carpels deeply imbedded into the locule with cavities (arrow) inside from the fused ventral bundles and basal parts of the ovules (asterisk). Fig. 16. TS through the middle part of the gynoecium, note the well-developed ovules, the fused margins of three adjacent carpels deeply imbedded into the locule and initials of the scales on outer surface. Fig. 17. TS through the distal fertile part of the gynoecium locule. Fig. 18. TS through the tapering distal part of the gynoecium locule. Scale bars, 1 mm (Figs 9–18). ᭣ locule, which is round at the transverse section compressed by the dramatically enlarged seed. The because of multiplication of the innermost zone of the seed is ovoid with six deep, longitudinal impressions mesocarp (Fig. 38). of the internal fruit ridges. The endocarp is partly At the third developmental stage, the fruit is obliterated. Thus, the innermost, parenchymatous approximately 4.5 cm in diameter and is elongate– and very thick zone of mesocarp developing inside the ovoid in shape (Table 2). In comparison with the pre- pyrene plays a very important role in the process of vious stages, further growth and lignification of the seed growth. It secures the development of the seed in sheaths of vascular bundles in the second topographic a fixed position in the centre. This soft parenchyma- zone of mesocarp is conspicuous (Fig. 52). In the third tous inner zone of mesocarp is easily compressed by zone of the mesocarp, the progressive thickening and the tissues of the growing seed (cf. Figs 38, 40). lignification of the cell walls starts. In the fourth, Because of this compression, the pyrene seems to be innermost zone of the mesocarp the parenchymatous the inner zone of the pericarp, which is actually not cells become larger and scattered secretory so. Our results clearly show that the pyrene in (etherealoil-containing?) cells become differentiated E. utilis fruits develops in the middle zone of the among them. The endocarp is represented by a single mesocarp, but not in the inner zone of the pericarp. A epidermal layer of thin-walled cells. The developing similar mode of fruit development and the structure seed fills the whole locule, which is circular in trans- of mature pericarp is revealed in E. minor and E. tris- verse section and similar to the second developmental tis (see Table 2). stage. At the fourth stage of development, the fruit Eugeissona insignis reaches its final dimensions, c. 5.1 cm in diameter In E. insignis the fruits are similar in shape to fruits (Figs 39–40). The pericarp is nearing final differen- of other Eugeissona spp. studied (Figs 39, 42), but an tiation (Fig. 41). By fruit maturity, the seed enlarges additional main inner group of vascular bundles dramatically and fills all the space inside the third develops and participates in pyrene formation zone of mesocarp (Fig. 40). The second zone of the (Figs 43–44), as mentioned above. In cross section, 12 mesocarp does not show dramatic changes in com- longitudinal ridges are clearly visible (Fig. 43). parison with previous developmental stages. The third zone of the mesocarp is made up of fibre-like sclereids with heavily thickened and fully lignified DISCUSSION walls (Figs 7–8). The sclereids form networks interlaced in different directions. Thus, this zone forms the GYNOECIUM STRUCTURE pyrene of the fruit composed of numerous networks of As in most palms and many monocots, the gynoecium sclereids. The peripheral networks are mostly longi- of Eugeissona is made up of three carpels. The tudinally and obliquely–radially elongated and the general plan of vascularization, and particularly the inner ones are obliquely–tangentially elongated. The position of the ventral bundles, suggests that fourth, innermost zone of mesocarp is substantially the gynoecium in Eugeissona can be referred to the

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Figures 19–30. Eugeissona utilis, microtome transverse sections (TS) of the third stage of gynoecium development [m1, the first (peripheral) zone of mesophyll; m2, the second zone of mesophyll; m3, the third zone of mesophyll; m4, the fourth (inner) zone of mesophyll; i, inner (locular) epidermis]. Fig. 19. TS through the distal part of the gynoecium, note the triradial slit in the centre (arrow). Fig. 20. TS through the distal part of the gynoecium with triradial slit in the centre, note the scales on gynoecium surface. Fig. 21. TS through the distal part of the gynoecium with triradial slit in the centre. Fig. 22. TS through the base of the style with triradial slit in the centre. Fig. 23. TS through the style with triangular slit in the centre, note the differentiation of three glandular slits. Fig. 24. TS through the style with triangular slit of the locule in the centre connecting to the ambient through the glandular slits. Fig. 25. TS through the distal part of the style made of three separated stigmatic lobes. Fig. 26. TS through the locule, note the differentiation of the gynoecium wall into several zones and parenchymatous fused margins of adjacent carpels with ventral vascular bundles; Fig. 27. TS through the central part of the locule, note the differentiation of the cavity between the fused distal parts of the margins of Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 adjacent carpels (arrow). Fig. 28. TS, close-up of Figure 18, note the differentiation of specific sheath around the ventral vascular bundles of the adjacent carpels (arrows) and numerous initials of the scales on the gynoecium surface. Fig. 29. TS, close-up of Figure 19. Fig. 30. TS, close-up of Figure 22, note the fragment of the triangular slit covered with epidermis and one of three glandular slits (arrow). Scale bars, 1 mm (Figs 19–21); 0,5 mm (Figs 22–25); 0.3 mm (Figs 26–30). ᭣ paracarpous type (Troll, 1928; Takhtajan, 1942, apocarpous gynoecium as the most archaic type for 1964). According to Endress (1994), the paracarpous angiosperms as a whole and the origin of coenocar- gynoecium is entirely symplicate. The symplicate pous gynoecia from it. In this way, primarily apocar- gynoecium of Eugeissona is topped with a distally pous Coryphoideae should be placed at the base of plicate style (the tips). Several distinctive features of Arecaceae as suggested in earlier systems (Drude, gynoecium structure in Eugeissona were revealed 1887; Moore, 1973; Uhl & Dransfield, 1987). However, during the present study: (1) the ovary wall is made recent phylogenetic investigations indicate that sub- up of numerous cell layers, comprising well-defined family Calamoideae is sister to all other palms topographic zones; (2) the gynoecium has a well- (Asmussen et al., 2006; Dransfield et al., 2008; Baker developed vascular system; (3) most histological ele- et al., 2009). Calamoideae is characterized by sympli- ments of fruits (including mechanical ones) cate (paracarpous) gynoecia, whereas apocarpous differentiate at early developmental stages and, in gynoecia occur in Nypoideae and Coryphoideae, two particular, the development of the pyrene of the fruit groups of relatively derived palms (Asmussen et al., already starts in the as-yet unpollinated gynoecium. 2006; Dransfield et al., 2008; Baker et al., 2009). The three isolated longitudinally elongate cavities Thus, could the gynoecium with free carpels be of developed inside the fused ventral bundles in the secondary origin in palms? This seems to be highly three largest inner gynoecial ridges are covered with probable in view of recent phylogenetic data (Asmus- epidermal cells and are treated as homologues of sen et al., 2006; Dransfield et al., 2008; Baker et al., septal nectaries (Figs 15–17, 27). The central protru- 2009), which show the palms to be a monophyletic sion of the inner floral base is the proliferation of the group. Moreover, most of the studied palm species floral axis, that can also be observed in the gyno- with trimerous syncarpous gynoecium have septal ecium, made up of free carpels at the locule level nectaries (Uhl & Moore, 1971; Cronquist, 1981; (Licuala Wurmb., Coryphoideae tribes Trachycarpeae Dransfield & Uhl, 1998; Stauffer, Rutishauser & and Livistoneae, Stauffer, Barfod & Endress, 2009). Endress, 2002; Rudall et al., 2003; Stauffer & The proliferation of the floral axis, which shifts the Endress, 2003; Stauffer et al., 2004; Askgaard et al., originally basal placentas upwards, is described for 2008; Takhtajan, 2009). This indicates that the fusion other representatives of palms (e.g. Pholidostachys of the basal parts of the carpels (ovaries) is postgeni- H.Wendl. ex Benth. & Hook.f and Asterogyne tal (Rudall, 2002; Stauffer et al., 2002, 2004). Excep- H.Wendl. ex Benth. & Hook.f., Arecoideae tribe tionally postgenital fusion is a particular feature of Geonomateae, Stauffer & Endress, 2003; Butia Becc., most syncarpous basal monocots (Igersheim, Buzgo & Arecoideae tribe Cocoseae, Uhl & Moore, 1971). Endress, 2001), and representatives of lilioid mono- The symplicate (paracarpous) gynoecium of Eugeis- cots (Hartl & Severin, 1981; Rudall, 2002). For all sona is described for all genera of Calamoideae and syncarpous palms, in which gynoecium morphogen- termed ‘incompletely trilocular’ (Dransfield & Uhl, esis has been studied, postgenital carpel fusion was 1998; Dransfield et al., 2008). Thus, the symplicate indicated for most of the carpel height (Rudall et al., gynoecium could possibly be a potential symplesio- 2003; Stauffer & Endress, 2003; Stauffer et al., 2004; morphy of subfamily Calamoideae. Bessey (1915), Askgaard et al., 2008). If the stage of postgenital Hutchinson (1973) and Takhtajan (1964) proposed the fusion does not occur, the carpels remain free, and the

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Figures 31–35. Microtome transverse sections (TS) of the gynoecium [m1, the first (peripheral) zone of mesophyll; m2, the second zone of mesophyll; m3, the third zone of mesophyll; m4, the fourth (inner) zone of mesophyll; i, inner (locular) epidermis]. Figures 31–33. Eu. utilis, the third stage of gynoecium development. Fig. 31. Close-up of Figure 18, the initials of the scales on the gynoecium surface made of epidermis and subdermal layers of cells, note the protovascular bundles of the gynoecium wall (arrows). Fig. 32. Close-up of Figure 19, the developing gynoecial scales. Fig. 33. Close-up of Figure 21, the mature gynoecial scales. Figures 34–35. Eugeissona insignis. Fig. 34. TS of the gynoecium at the fourth developmental stage, note the development of 11 (12 in type) internal ridges (arrows) inside from the circular part of the third zone of the mesophyll (mesocarp). Fig. 35. Close-up of Figure 34, note the differentiation of mesophyll (mesocarp) into four topographic zones and development of several layers of overlapping scales (arrow). Scale bars, 0.1 mm (Figs 31–33); 1 mm (Fig. 34); 0.5 mm (Fig. 35). syncarpous gynoecium transforms into a secondarily instances of reversal even in a highly specialized apocarpous one. It is highly probable that this loss of pseudomonomerous gynoecium; the free distal parts fusion took place in some representatives of Cory- of the carpels of Dypsis lokohoensis J.Dransf. could be phoideae; in Licuala postgenital fusion happens with treated as an example of such a reversal. Thus, the stylodia only, whereas the ovaries remain free free carpels of the fully developed gynoecium in palms (Stauffer et al., 2009) and the same is observed in in general or just in Coryphoideae could be of second- other genera of Trachycarpeae subtribe Livistoninae ary origin. Secondary apocarpy is also recorded for and in unplaced genera of Trachycarpeae (Dransfield other groups of monocots, for example, in Alismatidae & Uhl, 1998; Dransfield et al., 2008). The cases of (Dahlgren, Clifford & Yeo, 1985; Chen et al., 2004), postgenital fusion of nearly sessile apical stigmas are and is generally typical for monocots (Doyle & also recorded for apocarpous Rhapis L.f. (Trachycar- Endress, 2000). The gynoecium of fully fused carpels peae subtribe Rhapidinae; Giddey, Spichiger & of the symplicate type (Endress, 1994), typical for Stauffer, 2009, Fig. 3b, d). Rudall et al. (2003) admit Eugeissona, an early diverging lineage of Arecaceae,

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Figures 36–44. Morphology and transverse sections (TS) of fruits. Figures 36–41. Eugeisona utilis. Fig. 31. The young fruit (stage 1). Fig. 37. TS and longitudinal sections (LS) of young fruits from Figure 36, note the differentiation of mesophyll into four topographic zones and two aborted ovules (arrows), the largest pollinated ovule is removed. Fig. 38.The young fruit (stage 2), note the single developing ovule in the centre (arrow). Fig. 39. The mature fruit (stage 4). Fig. 40. TS, the mature fruit (stage 4), note the rigid internal ridges making invaginations in the mature seed. Fig. 41. TS, close-up of Figure 40, note the differentiation of mature pericarp, massive pyrene with one of six internal ridges (arrow) and sufficiently compressed innermost zone of mesocarp (asterisk). Figures 42–44. Eugeissona insignis. Fig. 42. The mature fruit. Fig. 43. TS of the mature fruit, note the 12 internal ridges, six principal ones and six additional smaller ones; endosperm is shrivelled, but some seen in the centre. Fig. 44. TS, close-up of Figure 43, note the differentiation of mature pericarp, and the complex structure of the pyrene. Scale bars, 1 cm (Figs 36, 38, 40, 43); 0.5 cm (Figs 37, 41, 44); 2 cm (Figs 39, 42).

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Figures 45–52. Microtome transverse sections (TS) of pericarp of Eugeisona utilis fruits developmental stages (exc, exocarp; fim, the first zone of mesocarp; sm, the second zone of mesocarp; tm, the third zone of mesocarp; fom, the fourth zone of mesocarp; enc, endocarp). Figures 45–48. TS of young fruit (stage 1). Fig. 45. Exocarp and three outer zones of mesocarp. Fig. 46. Close-up of peripheral zones of pericarp. Fig. 47. Inner zones of pericarp, note the invagination (internal ridge – see arrow) of the third zone of mesocarp containing ventral vascular bundles of the adjacent fused carpels in the fourth zone. Fig. 48. The innermost zone of mesocarp, note the regular rows of multiplying cells. Fig. 49. TS of young fruit (stage 2), the exocarp and three zones of the mesocarp. Fig. 50. TS of mature fruit (stage 4), the exocarp and two outer zones of the mesocarp. Fig. 51. TS of mature fruit (stage 4), the scale. Fig. 52. TS of immature fruit (stage 3). Scale bars, 1 mm (Figs 45, 49, 50, 52); 0.3 mm (Figs 46, 48, 51); 0.5 mm (Fig. 47). ᭣ Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 is contrasted with the synascidiate gynoecium made all four studied species of Eugeissona spp. The diag- up of fully fused carpels in which the ‘symplicate zone nostic features of development and mature structure is lacking’ (Stauffer & Endress, 2003: 197); this last of the Eugeissona pericarp are as follows. gynoecium type is typical for one of the most advanced group of palms, tribe Geonomateae 1 Exocarp and endocarp are poorly differentiated. (Stauffer & Endress, 2003). At the same time, it was The exocarp participates in the formation of the supposed by morphologists for different groups of scales and the endocarp is almost completely oblit- angiosperms (Joshi, 1947; Puri, 1952; Eames, 1961; erated in the mature fruit. Takhtajan, 1964) that the paracarpous (symplicate) 2 Differentiation of the mesocarp starts at the earli- gynoecium could have originated earlier than the est stages of development, de facto in the gyno- syncarpous s.s. (synascidiate) one. The trilete slit ecium before pollination. connecting the locule with the ambient (inside the 3 Four topographic zones of the mesocarp comprise style) and developing as a result of partial postgenital most of the pericarp: the peripheral zone forms the fusion of carpel margins is filled with secretory sub- main tissue of the gynoecial scales; the next zone stance that supposedly functions as a compitum. The contains numerous vascular bundles and forms the development of the paracarpous gynoecium in Eugeis- outer parenchymatous zone of the mesocarp; the sona is treated as the second mode of carpel closure, third zone is lignified and becomes the pyrene; of four types of carpel closure (Endress & Igersheim, the fourth, innermost zone consists of the inner 2000). parenchymatous zone that suffers dramatic crum- The gynoecial scales of Calamoideae are the most pling at maturity. obvious synapomorphic feature of the subfamily 4 The pyrene is made up of fibre-like sclereids com- (Dransfield et al., 2008). These scales are an adapta- prising large tightly packed and interlaced net- tion (supposedly relatively late) for protection from works oriented in different directions; the pyrene phytophageous insects with chewing mouthparts (e.g. includes bundles derived from the fruit vascular beetles). Morphologically, the gynoecial scales are out- system and additionally the larger dorsal (3), growths (emergences) covered with exocarp and made ventral (3 ¥ 2) and lateral vascular bundles of the up of several peripheral mesocarpal layers of cells fruit. (Bobrov et al., 2011). In Eugeissona, the gynoecial 5 Basipetal development of gynoecial scales, the epi- scales originate basipetally in more or less regular dermis of which is the exocarp and whose internal vertical rows, which soon lose their correct orienta- tissue is derived from the peripheral topographic tion, and the scales become irregular in distribution zone of the mesocarp. on the gynoecium surface. Later, with fruit growth, new rows of scales develop between the earlier differ- The fruit of Eugeissona could be referred to as a entiated rows. This feature is treated as archaic and monospermous pyrenarium of the Latania type – the autapomorphic for the subfamily. type of coenocarpous indehiscent fruit with the The placentation type (three basal ovules) in pyrene made of the central zone of the mesocarp Eugeissona and Calamoideae is potentially significant (Bobrov et al., 2009). for phylogenetic analysis, but has not yet been used. Eugeissona differs from other studied representa- This feature is a synapomorphy for the subfamily tives of Calamoideae [Calamus, Daemonorops Blume (Dransfield & Uhl, 1998; Dransfield et al., 2008). ex Schult.f., Raphia P.Beauv., Mauritia L.f and Mau- ritiella Burret- (A. V. F. Ch. Bobrov & M. S. Romanov, unpubl. data)] both in the mode of fruit development FRUIT STRUCTURE and in the structure of the pericarp at all stages of The general mode of fruit development and the struc- fruit development. The fruits of all other genera of ture of the pericarp in the mature fruit are similar in Calamoideae have no pyrene in the pericarp (Drans-

field & Uhl, 1998; Dransfield et al., 2008). The histo- of fruits mentioned above characterize the process of genesis of the pericarp in species of Calamus, pericarp histogenesis revealed by us in Nypa fruti- Daemonorops, Raphia, Mauritia and Mauritiella dra- cans Wurmb. (Nypoideae) and representatives of matically differs from that described for Eugeissona Borasseae: Bismarckia nobilis Hildebr. & H.Wendl., (A. V. F. Ch. Bobrov & M. S. Romanov, unpubl. data). Satranala decussilvae Beentje & J.Dransf., (These taxa are similar in the presence of gynoecial Hyphaene Gaertn., Medemia argun (Mart.) Würt- scales and non-specialization of a single-layered temb. ex H.Wendl., Latania, Lodoicea maldivica endocarp.) Fruits of these genera of Calamoideae are (J.F.Gmel.) Pers., Borassus (Romanov et al., 2011; A. characterized by a simple mesocarp structure differ- V. F. Ch. Bobrov & M. S. Romanov, unpubl. data). entiated into a peripheral zone, comprising the body The most significant difference in fruit structure in of the scales and the main parenchymatous zone with Nypa and borassoid palms from Eugeissona is the Downloaded from https://academic.oup.com/botlinnean/article/168/4/377/2416104 by guest on 27 September 2021 scattered vascular bundles. There is no differentiation absence of gynoecial scales, recognized as a synapo- of the mesocarp into other topographic zones during morphy in Calamoideae (Baker, Dransfield & Hed- gynoecium/fruit development; only the number of par- derson, 2000). The common features of pericarp of enchymatous cell layers increases (A. V. F. Ch. Bobrov Eugeissona, Nypa and Borasseae prevail over the & M. S. Romanov, unpubl. data). The fruits of different types of gynoecium: paracarpous, apocar- Calamus, Daemonorops, Raphia, Mauritia and Mau- pous and eu-syncarpous. The pericarp structure of ritiella (and in fact fruits of all other taxa of Calam- Eugeissona, Nypa and Borasseae could be the base oideae) are one- to three-seeded paracarpous berries for development (directly or indirectly) of other covered with gynoecial scales (making the structure of types of pericarp differentiation, revealed in differ- the berries more complex) (Bobrov et al., 2009; A. V. F. ent taxa of Arecaceae (Juliano, 1926; Biradar & Ch. Bobrov & M. S. Romanov, unpubl. data). In all Mahabale, 1969; Murray, 1973; Essig, 1977, 1999; these non-Eugeissona-type calamoid fruits, we can Essig & Young, 1979; Landsberg, 1981; Essig, distinguish two types, one in which the mesocarp is Manka & Bussard, 1999; Chapin, Essig & Pintaud, fleshy and the testa dry (Eremospatha, Korthalsia, 2001; Essig, Bussard & Hernandez, 2001; Essig & Laccosperma, Mauritia, Mauritiella, Metroxylon, Hernandez, 2001; Essig & Litten, 2004; Bobrov, Raphia) and the other in which the mesocarp is dry Romanov & Džalilova, 2007b; De Mendonca et al., and becomes thin at maturity, and the testa is devel- 2008; Vegas et al., 2008). The drupe of the Rhapis oped as a thick fleshy sarcotesta (Calamus, Ceratolo- type described for many coryphoid palms could also bus, Daemonorops, Eleiodoxa (Becc.) Burret, be derived as the result of reduction from the pyre- Lepidocaryum Mart., Myrialepis, Oncocalamus Mann narium of the Latania type with complex differen- & H.Wendl., Pigafetta (Blume) Becc., Plectocomia tiation of the pericarp (Murray, 1973; Bobrov et al., Mart. & Blume, Plectocomiopsis Becc., Pogonotium 2007a; Bobrov & Romanov, 2007; Bobrov et al. J.Dransf., Retispatha J.Dransf., Salacca Reinw.). 2008a). Thus, comparing the recent phylogenetic Nevertheless, the difference in pericarp structure data (Asmussen et al., 2006; Dransfield et al., 2008; (and fruit type) of Eugeissona and all other Calam- Baker et al., 2009) and our original results of mor- oideae is not such an insuperable problem for an phological studies, we suppose that the pericarp interpretation of Eugeissona and all other Calam- (and ovary wall) structure of Eugeissona, Nypa and oideae. The examples of progressive reduction of the Borasseae could be treated as unique to Arecaceae. pyrene (stone) in fruits were described for Arecaceae The distribution of anatomical structures of the taxa (Essig, 1977, 2002; Bobrov et al., 2008b) and for pericarp in these groups shows that it is probably other families of angiosperms (Bobrov et al., 2009). plesiomorphic for Arecaceae. The reduction of a sclerenchymatous stone/pyrene in the fruit is a rather common mode of fruit morphogenesis. So, recognizing the position of Eugeissona as ACKNOWLEDGEMENTS sister to other genera of Calamoideae (Asmussen et al., 2006; Dransfield et al., 2008; Baker et al., 2009), We thank Professor William L. Crepet, Edward Cope, we assume that the berries of most representatives of Sherry Vance and Sergei Isaev for their kind help Calamoideae originated as the result of pyrene reduc- with work with palm fruit spirit collection. We are tion in fruits of a Eugeissona type. In this case, much indebted to Dr Paula J. Rudall and Christina J. carpological data support the isolated position of Prychid who kindly provided the opportunity to work Eugeissona in Calamoideae. in the Jodrell Laboratory, Royal Botanic Gardens, The processes of pericarp development in Eugeis- Kew. We are grateful for the constructive criticisms of sona are similar to those in Nypa and borassoid three anonymous reviewers. The study was supported palms (Romanov et al., 2011; A. V. F. Ch. Bobrov & by the Russian Foundation for Basic Research (grant M. S. Romanov, unpubl. data). Features 2, 3 and 4 no. 08-04-01326-a).

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