Floral Organ Sequences in Apiales (Apiaceae, Araliaceae, Pittosporaceae)

Home , Aralia elata, Astrantia, Astrantia major, Eryngium, Eryngium campestre, Sanicula

Floral organ sequences in Apiales (Apiaceae, Araliaceae, Pittosporaceae)

P Leins and C Erbar*

Heidelberg Institute of Plant Sciences (HIP) — Biodiversity and Plant Systematics, University of Heidelberg, Im Neuenheimer Feld 345, D-69120 Heidelberg, Germany * Corresponding author, e-mail: [email protected]

Received 10 March 2003, accepted in revised form 24 October 2003

It is remarkable that families like Apiaceae and Reduction of the calyx and shortening of the plas- Brassicaceae, characterised by uniform floral diagrams tochrons toward zero are trends found in the more (i.e. stable positioning of floral organs relative to one advanced Apioideae (Foeniculum, Levisticum). another), show a great variability in initiation sequence Hydrocotyle, with its early sympetaly, resembles the of the floral organs. Within the subfamily Saniculoideae Araliaceae more closely. Of interest is the fact that in of the Apiaceae temporal overlaps in the initiation of the Araliaceae the flower orientation is variable. Sometimes floral whorls (Astrantia), the formation of common sta- one sepal is opposite the subtending bract, a feature men-sepal primordia (Astrantia), and segmentation in which becomes fixed in Cyphiaceae and Lobeliaceae of the formation of petals in pairs (Sanicula) occur. Campanulales, a sister group of Apiales.

Introduction

In Apiaceae, a family of the euasterids that is characterised tion of the petals 1, 2 and 3 as well as 4 and 5 tends toward by a nearly uniform floral diagram — the flowers are tetra- zero (Figures 1b–c). When all corolla primordia have been cyclic with an oligomerous gynoecium — we can observe a initiated, the stamens arise in a spiral sequence starting with great variability in initiation sequence of the floral organs. In stamen 1 in front of sepal 1 (Figures 1d–f). Finally two (or the past quite different and sometimes contradictory reports seldom three) carpels arise successively (Figures 2a–b). of the developmental patterns have been made (Payer Only the terminal flowers of the Eryngium inflorescence 1853, 1857, Jochmann 1854, Sieler 1870, Schuchardt 1881, show a constant spiral sequence. The lateral flowers of the Schumann 1890, Jurica 1922, Borthwick et al. 1931, Sattler inflorescence arise in the axil of bracts and vary somewhat 1973; for an overview of the former, mostly not illustrated in the sequence of their organ initiation: a continuous spiral descriptions see Erbar and Leins 1997, pp 55, 60, 61). sequence has never been observed. The members of corol- The best tool for studying organ sequences is the SEM. la and androecium whorls can overlap in their initiation (see The techniques used are described in several papers (e.g. Erbar and Leins 1985). Erbar and Leins 1989). A comparison of floral developmental patterns and how they relate to results from molecular Sanicula europaea sequence analyses provide a better insight into the phylogenetic relationships on a higher taxonomic level. In the flowers of Sanicula europaea, the five sepal primordia arise in spiral sequence (Figure 3a). Four petals are initiat- Floral Developmental Patterns in Saniculoideae ed successively in pairs in the sectors of the sepals 1 and 2 (Figures 3b–c). Together with the formation of the last petal

Eryngium campestre (P3 in Figure 3d) the first stamen becomes visible in front of sepal 1. Sometimes all petal primordia and the first stamen The terminal flowers in the cone-like inflorescence of may arise nearly simultaneously. The remaining stamen pri- Eryngium campestre show an almost continuous spiral mordia follow in a more or less distinct spiral sequence sequence of all organs, with the restriction that sepals, (Figures 3e–f). The two carpels are formed quickly after one petals, and stamens are nearly alternate (Figure 1). In young another. developmental stages it is striking that exact alternation is not achieved: the petal primordia are situated nearer to the Astrantia major older sepal primordium. Petal 1 is nearer to sepal 1 than to sepal 3, and petal 2 is nearer to sepal 2 than to sepal 4 In Astrantia major, the hermaphrodite and the functionally (Figure 1b). Additionally, the time interval between the initia- male flowers exhibit the same early pattern. The floral devel- South African Journal of Botany 2004, 70: 468–474 469

Figure 1: Eryngium campestre L. (a) Terminal flower with five sepal Figure 2: Eryngium campestre L. (a) Protrusion of a carpel (C) primordia (1–5). (b–c) Initiation of the petals (P). (d–f) Formation of between the stamens 1 and 3. (b) Gynoecium with three carpels stamens. Numbering according to the spiral sequence of the organs (white numerals). P = petal, S = sepal, St = stamen. From Erbar and (sepals labelled with large-size numerals, stamens with small-size Leins 1985 numerals). P = petal, St = stamen. From Erbar and Leins 1997 opment starts with the successive formation of three big pro- observe a decrease of the size of the small sepals corre- tuberances (Figure 4a), which in the same sequence then sponding to a 2/5 spiral sequence (Figure 6). During further each differentiate into a sepal primordium and a stamen pri- development the sepals do not enlarge and are not dis- mordium (Figure 4b). After the splitting of the three stamen- cernible in adult flowers. sepal primordia, petal initiation occurs, following a 1/5 spiral, starting with petal 1 between the sepals 1 and 3 (Figure 4c). Levisticum officinale Petal 4 originates nearly synchronously with sepal 4 (Figure 4d) and petal 5 with sepal 5 (Figure 4e). Then the spiral ini- Floral ontogeny in Levisticum officinale greatly resembles tiation of the androecium is continued with the stamen pri- that in Foeniculum vulgare. Whereas in the latter species a mordia 4 and 5 (Figure 4f). The two carpels arise in Astrantia distinct spiral sequence in the androecium can be observed, more or less simultaneously (not shown). the stamen primordia in Levisticum officinale are initiated in a more rapid succession (Figure 7). Floral Developmental Patterns in Apioideae Floral Developmental Pattern in Hydrocotyle Foeniculum vulgare This species differs strongly from those described above: no The primordia of calyx, corolla and the first stamen originate sepal primordia are initiated, and the petals arise simultane- more or less simultaneously in Foeniculum vulgare (Figure ously. After stamen inception — the stamen primordia arise 5a–b). The other four stamen primordia follow in a distinct in a rapid spiral sequence — the petals are connected by 2/5 spiral sequence (Figures 5c–e). Then the two carpel pri- low interprimordial shoulders (see Figure 3 in Erbar and mordia arise simultaneously (Figure 5f). Although all sepal Leins 2004). primordia become visible at the same time, later on we can 470 Leins and Erbar

Figure 3: Sanicula europaea L. (a) Spiral inception of the sepals Figure 4: Astrantia major L. (a) Protrusion of three common sta- (1–5). Primordia below the calyx are bracts. (b–c) Formation of men–sepal primordia (I–III), (b) Differentiation of the three stamen– petals (P) in pairs in the sectors of the sepals 1 and 2. Within a pair sepal primordia (I–III) into a sepal (large numerals) and a stamen one petal may have a weak temporal lead. (d–f) Spiral sequence in primordium (small numerals), (c–e) Initiation of the petals (P) in a the androecium (stamens labelled with smaller numerals). From 1/5 spiral, (f) Continuation of the spiral inception of the stamens (sta- Erbar and Leins 1997 mens labelled with smaller numerals). From Erbar and Leins 1997

Floral Developmental Patterns in Araliaceae are joined laterally by the time of initiation. These interprimordial areas scarcely enlarge in the later floral develop- The flowers of Araliaceae — Aralia elata (Figure 8a; see ment so that a very weak sympetaly is expressed in adult also Figure 2 in Erbar and Leins 2004), Hedera helix flowers (see Erbar and Leins 1995, 1996). (Figure 8e; see also Figure 1 in loc.cit.) — show a normal centripetal sequence of the whorls. From the beginning the Discussion petals are connected by a ring primordium (see Figures 1a–b, 2a–d in Erbar and Leins 2004). We have observed Comparing the ontogenies of apiaceous flowers investigated some variations in the sequence of the sepal primordia in this paper (see also Erbar and Leins 1985, 1997) we can (Aralia: compare Figures 8a–d; Hedera: compare Figures recognise the following trends with the aid of sequence dia- 8e–h). Sometimes the flower orientation can change in grams (Figure 9): such a way that one of the five sepals occupies an abaxial (1) shortening of the plastochrons in calyx, corolla and position (Figures 8d, 8h). gynoecium toward zero (extremely so in Foeniculum and Levisticum) Floral Developmental Pattern in Pittosporaceae (2) temporal overlap in the initiation sequence of calyx, corolla and androecium (especially in Astrantia) In Pittosporum tobira (Figure 4, Erbar and Leins 2004) and (3) formation of common stamen-sepal primordia in Sollya fusiformis (Figure 5, loc. cit.) all floral organs are initi- Astrantia ated in a strictly acropetal succession. The petal primordia (4) segmentation: i.e. formation of petals in pairs in Sanicula South African Journal of Botany 2004, 70: 468–474 471

Figure 6: Foeniculum vulgare Miller. Flower bud seen from below: spiral size decrease of the sepals. From Erbar and Leins 1985

Figure 5: Foeniculum vulgare Miller. (a) Young flower bud with five sepal primordia (indicated by arrows), five petal primordia (P), and the first stamen primordium (St1) formed nearly simultaneously. (b) Same flower bud as in (a) in side view; S = sepal. (c–e) Spiral sequence of the stamen primordia (1–5). (f) Formation of the two carpels (C). From Erbar and Leins 1997

(5) reduction of the calyx (Foeniculum, Levisticum, Hydrocotyle). It is remarkable that only the terminal flowers in the cone- like inflorescences of Eryngium campestre show a continuous spiral sequence of all organs. Presumably the spiral sequence in the terminal flowers may be influenced by the spiral programme in the inception of the bracts on the inflorescence axis: sepal 1 follows the last bract in the same divergence angle (Figure 10). Schuchardt (1881) already assumed that the spiral inception of the sepal primordia in Eryngium is related to the spiral appearance of the bracts. The overlaps in the sequence of the floral whorls especially in Astrantia may be correlated with the formation of three common stamen-sepal primordia, which originate in a spiral sequence. Following the A-B-C-gene-class-model we Figure 7: Levisticum officinale Koch. (a) Young flower bud with five may assume that the expression of the homeotic genes A, sepal primordia (S or indicated by arrow), five petal primordia (P), for determination of three sepals, and BC, for determination and three stamen primordia (St1–3) formed in a very rapid sequence. of three stamens in front of the three sepals, takes place (b) The fourth stamen primordium followed soon in spiral sequence. simultaneously. After the expression of the genes AB deter- (c) Spiral sequence of the stamen primordia (1–5) 472 Leins and Erbar

Figure 8: Floral developmental diagrams. (a–d) Aralia elata (Miq.) Seemann, (e–h) Hedera helix L. Diagrams (a) and (e) show the whole sequence, (b–d) and (f–h) refer only to the sequence and position of the calyx members. From Erbar and Leins 1988, modified

Figure 9: Overview of the floral developmental diagrams. The diagrams of Saniculoideae (at left) and Apioideae (at right) are each bordered. From Erbar and Leins 1985 South African Journal of Botany 2004, 70: 468–474 473

Figure 10: Eryngium campestre L. Top view of a young inflorescence: numbering of the organs according to their sequence; the smaller numerals (20–24) label the sepals of the terminal flower; the numerals 1–19 label the lateral flowers or bracts, respectively. From Erbar and Leins 1985

mining three petals, once more two sepals are determined by gene A and simultaneously the other two petals by the genes AB, followed by the expression of the genes BC determining the last two stamens (Figure 11). We only can make this assumption on condition that the appearance of the organ primordia coincides in time with the expression of the homeotic genes. Anyhow, the organ position — usually constant in Apiaceae flowers — seems to be regulated on a different level from that of organ sequence and that of organ identity. Figure 11: Top: Floral developmental diagram of Astrantia major. There are too little floral ontogenetical data available in Bottom: Schematic diagram of the A-B-C-gene model in which Apiaceae for detailed phylogenetic considerations. four whorl regions of a floral bud (1–4) are the domains of action Nevertheless, the Saniculoideae seem to have a higher (A, B, C) of three classes of homeotic genes (drawn after Coen plasticity in organ sequence than the Apioideae (Figure 9). and Meyerowitz 1991) In addition the inflorescences in Apioideae are more uniform than those in Saniculoideae (Figure 12; Froebe 1964, 1979, Weberling 1989): Whereas Eryngium campestre (Figure Lowry et al. 2001). As has been demonstrated (Erbar and 12a) has simple cone- or head-like inflorescences, complex Leins 1996, 2004), both Hydrocotyle and Araliaceae show inflorescences occur in Astrantia (Figure 12c) and Sanicula the precondition for early sympetaly, expressed in (Figure 12b). The complexity of Astrantia and Sanicula inflo- Dipsacales and Asterales s.l., which are sisters of Apiales. rescences is no longer visible in adult stages. They may be It is noteworthy that the flower orientation in Araliaceae derived from panicles or from panicles of umbellules — the can vary (see above, Figure 8). This indicates a tendency latter assumed to be an ancestral character state by Lowry becoming fixed in Cyphiaceae (Leins and Erbar 2003) and et al. (2001) — independently of the double umbels of Lobeliaceae (Erbar and Leins 1989) with one sepal in the Apioideae. It is noteworthy that in Apioideae transformation lower median plane of the flower. Both families belong to from monotelic to polytelic inflorescences takes place: in Campanulales within Asterales s.l. and with other characters Foeniculum vulgare, the umbellule does not develop a ter- the flower orientation can be used as evidence to support minal flower. the sister relationship between this order and the Apiales. The genus Hydrocotyle should be better placed next to Araliaceae not only due to molecular data (Plunkett et al. Acknowledgements — We are much indebted to the reviewers for 1996a, 1996b, 1997, Plunkett 2001, Downie et al. 2001, valuable suggestions on the manuscript. 474 Leins and Erbar

Erbar C, Leins P (1989) On the early floral development and the mechanisms of secondary pollen presentation in Campanula, Jasione and Lobelia. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 111: 29–55 Erbar C, Leins P (1995) An analysis of the early floral development in Pittosporum tobira (Thunb.) Aiton and some remarks on the systematic position of the family Pittosporaceae. Feddes Repertorium 106: 463–473 Erbar C, Leins P (1996) Distribution of the character states “early” and “late sympetaly” within the “Sympetalae Tetracyclicae” and presumably related groups. Botanica Acta 109: 427–440 Erbar C, Leins P (1997) Different patterns of floral development in whorled flowers, exemplified by Apiaceae and Brassicaceae. International Journal of Plant Sciences 158: 49–64 Erbar C, Leins P (2004) Sympetaly in Apiales (Apiaceae, Araliaceae, Pittosporaceae). South African Journal of Botany 70: 458–467 Froebe H (1964) Die Blütenstände der Saniculoideen (Umbelliferae). Eine vergleichend-morphologische und entwicklungsgeschichtliche Untersuchung. Beiträge zur Biologie der Pflanzen 40: 325–388 Froebe H (1979) Die Infloreszenzen der Hydrocotyloideen (Apiaceae). Akademie der Wissenschaften und der Literatur, Mainz. Abhandlungen der mathematisch-naturwissenschaftlichen Klasse. Tropische und Subtropische Pflanzenwelt 29: 501–679 Jochmann ECGG (1854) De Umbelliferarum structura et evolutione nonnulla. Dissertation Vratislaviae, The British Library Jurica HS (1922) A morphological study of the Umbelliferae. Botanical Gazette 74: 292–307 Leins P, Erbar C (2003) The pollen box in Cyphiaceae (Campanulales). International Journal of Plant Sciences 164 (5 Suppl.): S321–S328 Lowry PP II, Plunkett GM, Oskolski AA (2001) Early lineages in Apiales: insights from morphology, wood anatomy and molecular data. Edinburgh Journal of Botany 58: 207–220 Payer J-B (1853) Organogénie des familles des Myrtacées, Punicées, Philadelphées, Loasées et Ombellifères. Annales des Figure 12: Young inflorescences. (a) Eryngium campestre L. Spiral Sciences Naturelles. Botanique, Sér. 3, 20: 97–128 sequence of the flowers on a cone-like inflorescence axis. (b) Payer J-B (1857) Traité d’organogénie comparée de la fleur. Sanicula europaea L. Formation of bisexual (Z, E) and male (m) Masson, Paris flowers. T, t = bract. (c) Astrantia major L. At the basis of the Plunkett GM (2001) Relationship of the order Apiales to subclass inflorescence bisexual flower primordia (Z) are surrounded by male Asteridae: a re-evaluation of morphological characters based on flower primordia (m). (d) Foeniculum vulgare Miller. Spiral sequence insights from molecular data. Edinburgh Journal of Botany 58: of the flowers of an umbellule. The flower primordia are numbered 183–200 according to their initiation sequence. (e) Levisticum officinale Plunkett GM, Soltis DE, Soltis PS (1996a) Higher level relationships Koch. Young umbellule with enlarged central flower. (f) Hydrocotyle of Apiales (Apiaceae and Araliaceae) based in phylogenetic vulgaris L. Bracts (T) and their axillary buds are formed in a spiral analysis of rbcL sequences. American Journal of Botany 83: sequence (numbering). From Erbar and Leins 1985 499–515 Plunkett GM, Soltis DE, Soltis PS (1996b) Evolutionary patterns in Apiaceae: inferences based on mat K sequence data. Systematic References Botany 21: 477–495 Plunkett GM, Soltis DE, Soltis PS (1997) Clarification of the rela- Borthwick HA, Philipps M, Robbins WW (1931) Floral development tionship between Apiaceae and Araliaceae based on mat K and in Daucus carota. American Journal of Botany 18: 784–796 rbcL sequence data. American Journal of Botany 84: 565–580 Coen ES, Meyerowitz EM (1991) The war of the whorls: genetic Sattler R (1973) Organogenesis in Flowers. University of Toronto interactions controlling flower development. Nature 353: 31–37 Press, Toronto and Buffalo Downie SR, Plunkett GM, Watson MF, Spalik K, Katz-Downie DS, Schuchardt PO (1881) Beitrag zur Entwicklungsgeschichte des Valiejo-Roman CM, Terentieva EI, Troitsky AV, Lee B-Y, Lahham Blüthenstandes und der Blüthen der Umbellifloren. Dissertation J, El-Oqlah A (2001) Tribes and clades within Apiaceae subfami- Rostock. Engelhardt, Leipzig ly Apioideae: the contribution of molecular data. Edinburgh Schumann K (1890) Neue Untersuchungen über den Journal of Botany 58: 301–330 Blüthenanschluβ. Engelmann, Leipzig Erbar C, Leins P (1985) Studien zur Organsequenz in Apiaceen- Sieler T (1870) Beiträge zur Entwicklungsgeschichte des Blüten. Botanische Jahrbücher für Systematik, Pflanzengeschichte Blüthenstandes und der Blüthe bei den Umbelliferen. Botanische und Pflanzengeographie 105: 379–400 Zeitung (Berlin) 28: 361–369, 377–382 Erbar C, Leins P (1988) Blütenentwicklungsgeschichtliche Studien Weberling F (1989) Morphology of Flowers and Inflorescences. an Aralia und Hedera (Araliaceae). Flora 180: 391–406 Cambridge University Press, Cambridge

Edited by B-E van Wyk and PM Tilney