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ISSNOOOI-6799 Acta Phytotax. Geobot. 50(1): 59-73(1999)

Floral Morphology and Viztsculature of Schizopepon bryQniaefolius ()

" 2 TATSUNDO FUKUHARAi and JUNICHI AKIMOTO

iGraduate schoot ofHuman and Environmental Studies, K),oto University, K},oto 606-8501 2Centerfor EcologicalResearch, j<),oto University, Kbeoto 606-8502

AbstracL FIoral characters of an annual andredioecious Schizopepon bryoniaefoJius are with special reference (Cucurbitaceae--Schizopeponeae) described ,to the arrangement of stamens and ovary locules, vasculature, nectaries, trichomes and phenology. Both hermaphrodite and ma]e bear two dithecal and one monothecal stamens, as in many taxa of Cucurbitoideae, However, S, bryoniaojbtius differs from them in that each stamen is recognized as a single mound in an early stage of the development and receives a single vascular

bundle. The anther trichomes are snowman-ljke and are different in cell shape from those of the other previously examined taxa, There is no er small time-lag between anther dehiscence and stigma maturation in hermaphrodite fiowers, In both of the sexual morphs, there is a nectary at

the bottom of the receptacular cup.

Key words: androdioecy, Cucurbitaceae, fioral anatomy, Schizopqpon

Received February 5, J999, acceptedt"prit IO, 1999

The present study describes floral characters of a cucurbitaceous annual vine Schizopepon bryoniaojbtius Maxim. (Cucurbitaceae-Cucurbitoideae- Schizopeponeae) with special reference to the arrangement of floral components, vasculature, nectaries, stomata and trichomes. Two aims are intended by these observations. The first is to support or refute the current taxonomic position of the Schizopepon by floral characters. Recent systems treat Schizopepon either as the only genus of Cucurbitoideae-Schizopeponeae (Jeffrey, 1980, 1990; Lu and Zhang, 1985) or under Cucurbitoideae-Melothrieae-Sicydiinae (Lu and Zhang, 1986). Jeffi:ey (1964) established Schizopeponeae based on the observation that the pollen grain surface of Schizopepon is reticuloid (retipilate, in the sense of Punt et al. [1994] and Hoen [1998]), a unique feature in the family. However, judging from the data of Lu and Zhang (1985), it is not reticuloid but reticulate with spinulose muri and thus the isolated position of the genus is not supported

"Present address: c/o Mr. Satake, Ichijoji-Saikata-cho 7, Sakyo-ku, Kyote 606-8157. e-mail: [email protected]

Labels for the fioral vascular bundles. DA: dithecal stamen bundle; GD: carpel dorsal bundle (=stigma bundle) ; GV: carpel ventral bundle (=ovary septum bunclle) ; MA: monothecal stamen bundle; PC: central bundle of the corolla lobe; PL: lateral bundle of the corolla lobe; S: ca]yx lobe bund]e, The bund]es that

diverge into more than one bundle in the upper level of the are designated by linear formulas of the

"S+2PV'). labe]ings (e,g,,

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by explicit synapomorphies but by the combination of characters (Lu and Zhang, 1985). Schizopqpon and Sicyoeae (=Melothrieae-Sicydiinae) share a solitary pendulous ovule per locule, whereas other floral characters of Schizopepon are not shared by Sicyoeae but by the rest of Cucurbitoideae, namely, the androecial architecture composed of two dithecal stamens and a monothecal ene arranged "2+2+1 in a whorl (referred to as type"), tricolporate pollen grains with reticulate surface and 3-locular ovaries (Lu and Zhang, 1985, 1986). A close study on floral characters might provide infOrmation for the issue. The second aim concems the functional aspects of fiowers in relation to the androdioecious sexual system of Schizopepon bryoniaqfblius. A recent examination revealed that some of the populations of the species are androdioecious (Akimoto et al., 1999; earlier suggested by Makino [1940], Ohwi [1953], Kitamura et al. I1957], and Lu and Zhang [1985]). This is a very rare condition among angiosperms, and there are no more than five suflliciently documented examples (see Ishida and Hiura [1998] and Akimoto et al. I1999] for review). We therefbre examine the aspects of floral characters that may be functionally related to the reproductive ecology, and attempt to compare the characters with those of the few other androdioecious species.

Materials and methods

Flower sarnples were collected from two localities, Oguchi-mura, Ishikawa pref. and Kiyomi-mura, Gifu pref., both in central Japan. The populations were androdioecious in the former locality but hermaphrodite in the latter. The samples were fixed in FAA (water: ethanol: fbrmalin: acetic aci,d=9: 9: 1: 1 in volume). Paraffin sectioning and the preparation for SEM observation fbllowed conventional procedures. Moral vasculature was described based on the serial cross sections (at 10-15 pm in thickness) of 10 hermaphrodite flowers and five male flowers. Because there was no significant difference between the two localities in the observed characters of the hermaphrodite flowers, the localities are not mentioned in each part of the results. The text fo11ows the tribal and generic definition of Jethey (1990).

Results Injlorescence - Hermaphrodite At each fertile (flower-bearing) node, the subtends a solitary fiower, a dwarf flowering shoot and a tendri1 (Fig. IA, B). The dwarf shoots have a solitary flower at each node, short intemodes and small , and appear simi1ar to . The solitary flower usually blooms when the dwarf shoot at the node is not yet extended (Fig. IA). - Male plants An ebracteate , a raceme-bearing shoot and a tendril are subtended at each of the fertile nodes (Fig. IC). The raceme-bearing shoots spirally bear ebracteate racemes that are not subtended by a bract but occasionally some nodes in the upper part show branchings with three to five branches and a small subtending fbliage leaf. Thus they may be described as

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ole ri[

(primordiuaL}

FiG. 1. Semidiagrams illustrating flower-bearing nodes of Schizopepon br[yoniaojiolius. A, B, herrnaphrodite plant; C, Male plant. Arrows indicate the courses of the ,

double-racemes alternatively. Flower - Hermaphrodite flowers The receptacles are green and cup-shaped (Fig. 2B) and the upper part forms a low (O.2-O.5 mm) hypanthium (Fig. 2A), that continues to the calyx and white corolla. Both corolla and calyx have a short (less than O.5 mm) tube and five lobes. Corolla lobes are quincuncially arranged rllhree befbre opening (Fig. 5A). stamens, two dithecal ones and a monothecal one, are inserted at the base of the hypanthium (Fig. 2B). Filaments have round to elliptic cross sections (Fig. 5A, B) and are continuous to the slightly thickened anther connective, which contains a cluster of cytoplasm-rich cells (Fig. 2B). Anther thecae are alternate to the corolla lobes (Fig. 2B) and are attached to the abaxial sides of the connectives (the anthers are extrorse). Each theca has two locules and dehisces by opening an abaxial longitudinal slit (Fig. 2C). The anthers and the stigmas are located close to each other. An inferior 3-locular ovary is present below the receptacle (Fig. 2A, B), and a style protmdes from the center of the receptacular bottom and continues to three stigmas, each of which is further bilobed by an apical cleavage (Fig. 2C, 7A). The base of the style has a narrow (ca. 100 um in width) nectary zone with densely distributed stomata (Fig. 7A, B). In nectary zone, each stoma occupies the apex of mound-like convexities en the surface (Fig. 7B) and the underlying mesophyll cells contain dense cytoplasm befbre the corolla opens (Fig. 2B, arrowhead). Ovaries have triangular cross sections (Fig. 5E). Each of the three sides has a central longitudinal rib or two longitudinal ribs, depending on the number of the vascular bundles (Fig. 5E). The position of floral parts in relation to the axis could not be determined due to the complex architecture of the nodes (Fig. 1A, B). When the flower buds are less than 250 pm in diameter (Fig. 4A-I), calyx lobes (I-V in Fig. 4A-I) enclose the corolla lobes (1-5 in Fig. 4A-I). The future ovary locules are recognized as a trilobed furrow (s, t and u in Fig. 4A-I) and the androecium is composed of three mound-like (when the buds are less than 200 stm) to clavate (200-250 pm, Fig. 4A-I) stamen primordia (a, b and c in Fig. 4A- I), that are not significantly diflierent from each other in size and shape. In these stages, the stamen primordia are placed opposite a calyx lobe (a--I in Fig. 4A-I, respectively) and two corolla lobes (b--3, and c--4 in Fig. 4A-I), respectively.

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2

ig ,g

FiG. 2. Hermaphrodite flowers of Schilopepon besonianjioltus. A. Bucl shoray before opening. The portion of the cerolla surface (arrow) is enlarged in Fig. 7D. B, Longitudinal section of a bud. C. Floral center when bath stamens ancl stigmas are functional, D, Stigma sudece at maturity. E. Close-up of Fig. 2D, showing conical cell surface and germinating pollen grains. Scales = 1 rnm (A, B), 250 "m (C) ; 100 pm (D) ; 1Opm e).

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August 1999 FUKUHARA & AklMOIOI"'Flbfaa"tifititomy bf Schizqpepon 63

The future ovary locules alternate with the stamen primordia. wnen the buds are ca. 300 pm in diameter (at microspore mother cells stage), the anthers and the connectives are differentiated from each other. Of 30 opened hermaphrodite flowers, five have stigmas that are not receptive and anthers that are not dehiscent. In these fiowers, the stigmatic lobes (Fig. 5A, B) do not extend yet and have colliculose surfaces on which there is no pollen grain stuck to it. Twenty-one fiowers have dehiscent anthers and receptive stigrnas (Fig. 2C) ; the stigmas are deeply bilobed and have papillose surfaces, where each cell surface conically protrudes. There are frequently germinating pollen grains stuck to the stigma papillae (Fig. 2D, E). Three flowers have dehiscent anthers but immature stigmas, and one flower has indehiscent anthers and receptive stigmas. During early ftuit maturationi the anther connectives and stigmatic lobes are collapsed, but the calyx, corolla and stamens remain intact. - Male flowers One of the calyx lobes is adaxial to the raceme axis (Fig. 6A). Corolla, calyx and stamens do not significantly differ from those of hermaphrodite flowers (Fig. 3A, B), except that the stamens are insertpd at nearer the receptacle center ('Fig. 3B). There is a nectary zone (100-150 ym in diameter) surrounded by the filament bases at the center of the upper surface of the receptacle. The nectary zone has numerous stomata (Fig. 3C) and cytoplasm- rich underlying tissue (Fig. 3B, arrowhead) as in hermaphrodite flowers, but the stomata are not protruding (Fig. 3C). There is no vestigial style or ovary in male fiowers (Fig. 3B). In the buds that are less than 250 pm in diameter (Fig. 4J, K), there are three mound-like to clavate stamen primordia (a, b andc in Fig. 4J, K) at the bottom of the receptacle. lthsculature The vasculature is described by tracing the bundles in each floral component basipetally. - Hermaphrodite flowers In cross sections of the anther and style level (Fig. 5A, B), there is a single bundle in each of the calyx lobes ("S"), stamens "MA") ("DA" or and stigmas ("GD"), while each corolla lobe has three bundles (one central ["PC"] and two lateral ["PL"] ones). The S bundles are unbranched throughout, while the three bundles in the corolla lobe (a PC and two PL bundles) are sparsely fbrked and anastomose in the distal part of the lobes. The GD bundles are apically bifid and the two branches enter different stigma lobes. Near the upper edge of the hypanthium (Fig. 5B), each S is fused with the two neighboimg PL bundles to form an S+2PL bundle (compare Fig. 5B with 5C). Consequently, the hypanthium has 10 bundles (five PC and five S+2PL bundles). Shortly below, each of the stamen bundles (two DA and an MA bundles) is fused with either of the 10 bundles. In seven of the 10 observed flowers, each 1's fused with a PC (Figs. 5C-E, 6C). Three herrriaphrodite flowers show a different pattern in that the MA bundle is fused with the S+2PL bundle that does not neighbor the two DA+PC bundles (indicated by a dotted line in Fig. 6C). At the base of the receptacle (Fig. 5C), a PC and a S+2PL bundles･ are fused with each other ("S+2PL+PC" near the lower-right corner of Fig. 5D). An additional fusion of a PC and an S+2PL bundles takes place occasionally (in two

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RG 3 Male fiowers ef Schizopepon bryoniaqt?)lius A Cross section B Longitudrnal sectson C Surface of nectary (arrowhead in 3B) ant anther anc anther connective cal calyx lobe col corolla lobe hyp hypanthium Scales = O 5 mm B) 25 (A, , um (C)

samples). Consequently, there are eight or nme bundles in the outermost whorl (Fig 6C) rn the cross sectaons at the middle of the ovary (Fig 5E), each GD bundle is fused either with ("S+2PL+GD" at the upper corner in Fig 5E), or comes very "S+2PL+PC" close to ("S+2PV' and at the two lower corners in Fig. 5E), or rarely subststutes the confronted bundle in the outer whorl In one flower, a PC bundle (the underlmed one m Fig 5C), termmates blmdly at this level In the

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s lj

a

lp W " tii.

te bt i/att.

t;l. v

n/

'p{ua

l.twtSg'vvJt tt l

ees' kevgee

atvm' -'

FIG4 Senal longitudrnal sections of a yotmg flower bud of Schizopepon bryontaojblius A I Hermaphrodite flower J, K Male flower I-V pnmordial ca]yx lobes 1-5 pnmordial corolla lobes a-c primordial stamcns s-u future ovary locules Scale = 100 um for A I and 50 ym for J and K

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.'i "/ th /t /tf' }. '･i'3?lrz;ttl'･trS'3:,,g:'Sg;"

. di {

RG 5 Cross sectsons ofahermaphrodite fiowe of Schizopepon bryoniaojbliusr, showing vasculature A The basal parts of the corolla and calyx lobes B The upper part Df the hypanthium C TIhe base of the reLeptacle D The apical part of the ovary E The middle part of the ovary Scale = 1 mm

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S+2PL x o

L ssges tw c L A C

FIG. 6. A, B. Floral diagrams of male (A) and hermaphrodite (B) fiowers of Schizopepan br),oniaefolius. C. A diagram indieating vasculature in hermaphrodite fiowers at the level of hypanthium (cf, Fig. 5B). Arrows indicate the derivation of the staminal and stigma bundles. Solid and dotted ones indicate more common and rarer alternative patterns, respectively.

central axis of the ftuits, there are three bundles running through the ovary septa below the level of its distal part ("GV" in Fig. 5C, D). They terminate at the upper part of the ovary. The bundles in the center and the outer whorl converge at the base of the ovary into two to fbur bundles in a whorl. - Male flowers The floral vasculature (Fig. 3A) is identical to that of the hermaphrodite flowers except for the fo11owing points. Each of the DA and MA bundles is fused with a PC bundle. Neither GD nor GV bundle is present. The 10 bundles in the hypanthium converge into two to four bundles in a whorl at the base of the receptacle.

7beichomes and stomata Three types of floral trichomes are observed. The first is a capitate glandular one (arrow in Fig. 7D), comprising a stalk of 1-3 cells in a row and an ovate head of 2-8 cytoplasm-rich cells in 1-4 rows. These trichomes are densely distributed on both adaxial and abaxial surfaces of the corolla lobes (Fig. 2A), the adaxial surface of the hypanthium (Fig. 7A) except for the nectary zone. The abaxial surface of the calyx also shows this type, but very sparsely (Fig. 2A). The second type is a linear non-glandular hair of 2-4 cells in a row (arrowhead in Fig. 7D). The cells are uniform in width, but are longer in more apical ones. This type is found on the abaxial surface of the receptacle, pedicel, along the midrib of the abaxial surface of the corolla lobes and along the ribs and angles of the ovary surface. Both of the above two types are also common on vegetative parts. The third type is snowman-shaped hairs (Fig. 7C) composed of two (rarely three) serial spherical cells, of which the basal one is much 1arger than the upper. These hairs are present only on the anther and the anther connective near the upper' margin of the anther connective in a cluster of 5-10. In all the three types, the cells have a smooth surface. Stomata are densely and almost exclusively distributed in the nectary zones (Fig. 3C, 7A, B). The receptive regions of the stigmatic lobes often (15 of 22 exarnples) have one to three stomata (Fig. 2D, arrowhead). In a few flowers, the abaxial surface of the calyx has stomata sparsely.

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fiG. 7, Nectarics and trichornes oi hermaphrodite flowers of Schizopepon bo'oniaqfolius. A, The central part of a fiower, thc stamens removed except the base (S) ; stigmas immature. B. Nectary surface (urrowheads in Fig. IB and an arrow in Fig. 7A). C. Snowman-shaped trichomes on anthers (ant) and anthcr connectivc (anc). D. Capitate glandular (arrow) and linear non-glandular (arrowhead) trichemes on the abaxial side of corollalobes (arrow in 2A), Scales = 1OO pm (A. C, D) ; 20 pm (B).

Discussion

Comparison with the other Cucurbitaceae: Androeci"m architecture and vasculature Floral diagrams of Schiz(?pepon bryoniaefblius (Fig. 6A, B) generally agree "2+2+1 with that of the Cucurbitaceae with androecia of type" and trilocular ovaries; the three starnens nearly opposite the ovary locules, and the five thecae alternating with the corolla lobes, respectively. In the male fiowers of S. bryoniaeflolius, the arrangement of the anthers is oblique in relation to the raceme axis; the angular divergence subtended by the line from the raceme axis to the monothecal stamen via the floral center (X in Fig. 6A) approximates to

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72e . This angle is commonly observed in other cucurbitaceous taxa ( [Melothrieae], Heimlich, 1926; [Cucurbiteae], [], [Benincaseae], Eichler, 1875; [Jolffieae], Zimmermann, 1922; T7ichosanthes [Trichosantheae], Chakravarty, 1958),

although differentvalues are known from MomonticalLuLfiiz(Benincaseae,Oe, o

Chakravarty, 1958;'Zimmermann,-1922), (Benincaseae,180 , e -

Chakravarty,1958) and Cucu,nis (216 , Eichler,1875; Chakravarty,1958). This obliquity is present in six different tribes of Cucurbitoideae and is suggested to represent a relatively primitive condition of the subfamily. Each of the staminal bundles (DA or MA) is derived from a central bundle of the corolla lobe (PC) or rarely a calyx lobe bundle (S) in the receptacle (Fig. 5C, 6C). Although not many studies explicitly describe the origins of the staminal bundles, the bundle for each stamen i,s derived from one of the corolla or calyx Iobe bundles in Cucumis (Heimlich, 1927; Judson, 1929; Chakravarty, 1958) and Cucuthita (Chakravarty, 1958). On the other hand, Schizqpepon bryoniaojblius shows the characters in vasculature and early ontogeny that are unknown from, or rare in; the other "2+2+1 Cucurbitaceae with type" androecia. Both dithecal and monothecal stamens have a single bundle throughout (Fig. 5A-D). The androecium in young bud is recognized as three protuberances (Fig. 4A-K). Chakravarty (1958) showed in 10 cucurbitaceous genera that dithecal stamens have two bundles at the base while monothecal one has a single bundle, i.e., the androecium has five bundles. Ontogenetic studies on several genera showed that an androecium is initiated as five swellings and later comes to appear as three staminal primordia by intercalary growth in two of the five interthecal regions (Cucumis, Goffinet, 1990; Lagenaria, Imaichi and Kobayashi, 1989; Ltg61a, Imaichi and Uchibori, 1992; [Sicyeae], Imaichi and Okamoto, 1992). These observations 1argely "2+2+1 support the hypothesis that the type" androecia are derived from the state with five monothecal stamens as is found in some Cucurbitaceae (Chakravarty, 1958). On the other hand, dithecal stamens with a single bundle have been reported in (Benincaseae; Zimmerman, l922; Bhuskute et al., 1986; Deshpande et aL, 1986), M"kia (Melothrieae; Deshpande et al., 1986, as ) and (Melothrieae; Fukuhara, pers. obs.). Benincasa (Benincaseae) also has three dithecal stamens. For this genus, Chakravarty (1958) stated that the stamen bundle number is 2+2+1 in his Tlable 1 (p. 68) but drew a single bundle in each stamen in his Fig. 70 (p. 77) in agreement with the suggestion of Imaichi and Uchibori (1992). Partly because there is no ontogenetic data fbr the above genera, it is controversial whether the androecial type with three dithecal stamens in these taxa is derived from the more common "2+2+1 type" or has a different origin (Bhuskute et al., 1986; Chakravarty, 1949, 1958; Imaichi and Kobayashi, 1989). The state of Schizopepon could be C`2+2+1 regarded as an intermediate between the type" androecia and that of 'the M"kia-Zehneria-Coccinia(-Benincasa), and might suggest that latter is derived from the former. Another explanation is that the similarity between Schizopepon and Mukia-Zehneria-Coccinia(-Benincasa) represents a convergence accompanied by simplifications (or lack of complicacy) and are causally correlated with the smal1 anthers. In the taxa from which two bundles per dithecal stamen are reported, the anther thecae are }anger, and conduplicate or

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folded in more complex manners. In these.taxa, the staminal bundles are significantly 1arger than the other bundles in the receptacles in cross sections (Chakravarty, 1958; Heimlich, 1927; Imaichi and Kobayashi, 1989; Imaichi and Uchibori, 1992), whereas the staminal bundles of Schizopepon are not different from the other receptacular bundles in size (Fig. 5B-D). Zehneria and Mukia possess small unfolded thecae as does Schizopepon, but Coccinia (and Benincasa) has sinuous thecae. In Cucumis sativus L., the two dithecal stamens of the male flowers have two bundles (Heimlich, 1927), whereas the staminodes of the female flowers each have a single bundle (Judson, 1929), probably representing the function-related variation in the number of the bundles. More intensive studies on the cucurbit species with small anthers are necessary to extend this discussion.

Comparison with the other Cuc"rbitaceae: 77ichomes and nectary According to the classification of cucurbitaceous trichomes presented by Inamdar et al. (1990), Schizqpepon hryoniaefblius has J-type non-glandular and S-type glandular trichomes. Both types are commonly fbund on the flowers as well as vegetative parts in at least six different tribes (Inamdar et al., 1990; Zimmerman, 1922). Many cucurbitaceous taxa have anther trichomes or anther-connective trichomes (Inamdar et al., 1990; Zimmerman, 1922). The trichomes usually differ from those'on the other part of the plant in having a 1arger basalmost cell than distal cells. The snowman-like trichemes of Schizopepon is included in these categories of trichomes. In the hitherto known species, the basalmost cell is ovate and distal part is composed of a conical cell with an acute apex (e.g., Cucumis, Zimmerman, 1922; Ibervillea [Melothrieae], Dieringer and Cabrera, 1994) or by itself forrns a glandular or non-glandular trichome of various shape (g.g., Momontica, Zimmerman, 1922). Snowrnan-like trichomes composed of spherical cells differ from these and may be valuable for inferring the phylogenetic position of the genus, when further comprehensive data on the trichomes of Cucurbitaceae would be compiled. SchizQpepon flowers possess the nectary zone recognized by the cytoplasm- rich mesophyll cells and densely distributed stomata. In both male and hermaphrodite flowers, the nectary is concealed by the broad filaments as in Coccinia and Lq17la (Zimmerman, 1922).

Nbtes onjunctional aspects ofSchizopepon.flowers Among the examined hermaphrodite flowers, we could not detect any significant tendency of protoandry or protogyny. Our sampling was not suthcient for detecting small time difference of maturation between the sexes and more intensive sampling of newly opened flowers might draw different results. However, functional stages of the both sexes are largely overlapping and there is, if any, small phenological difference between the sexes in each hermaphrodite flower. Akimoto et al. (1999) reported that hermaphrodite flowers are self- compatible. The phenological overlaps, self-compatibility, and closely positioned stigmas and anthers can explain the high degree of inbreedin g when the populations lack male plants (Akimoto et al., 1999). In contrast, an oleaceous androdioecious species, flr( rinus lanuginosa Koidz., shows the combination of

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significantly protogynous phenology, selfsterility and low level of inbreeding (Ishida and Hiura, 1998). The few androdioecious examples of angiosperms differ from each other in pollination systems, and may have evolved under different selective regimes. Those in Phitlyrea (Oleaceae), Mercurialis (Euphorbiaceae) and Datisca (Datiscaceae) have been reported to be necterless and wind-pollinated (Traveset, 1994; Liston et al., 1989; Pannell, 1997) and F7ctxinus lanuginosa nectarless and both insect- and wind-pollinated (Ishida and Hiura, 1998). In E lanuginosa, the pollen grains of the hermaphrodite flowers are less vigorous than those of the male flowers and suggests that the reward or advertisement to pollinators might be an advantage of having pollen or pseudopollen for the hermaphrodites (Ishida and Hiura, 1998). Similar explanations have been suggested for the evolution of apparently androdioecious but functionally dioecious ("pseudoandrodioecious") species, many of which are insect-pollinated but lack the nectary (Mayer and Charlesworth 1991). However, both male and hermaphrodite fiowers of Schiiopepon hryoniaefolius have a nectary at the bottom of the receptacle, and thus the above hypothesis is not 1ikely to explain the evolution of androdioecy of Schizopepon.

The first author would here ]ike to memorize the second auther, Junichi Akimoto (1973- 1998), who drew his attention to the subjects, collected samp]es and encouraged him in initial phases of the study, He thanks the parents of J. Akimoto for their permission to publish this paper as it is. The authors are indebted to Hiroshi Tobe and Kihachiro Kikuzawa fbr their help and

encouragement, and to two anonymous reviewers for critical comments on the manuscTipt.

References

Akimoto, J., T, Fukuhara and K. Kikuzawa, 1999. Sex ratios and genetic variation in a functionally androdioecious species, Schizopepon bryonia(:folius (Cucurbitaceae). Amer. J. Bot. 86: 880- 886.

Bhuskute, S. M., K. H. Makde and P. K. Deshpande. 1986. Staminal organization in Coccinia grandis (L.) VoigL Ann, Bot, 57: 415-4]8, Chakravarty, H. L, 1949. Morphelogy of the stamiriate flower of bottle , Lagenaria teucantha (Duch,) Rusby. New Phytol. 48: 448-452. . 1958. Morphology of the staminate fiowers in the Cucurbitaceae with special reference to the evolution of the stamen, Lloydia 21: 49-87. Deshpande, P. K., S. M. Bhuskute and K, H, Makde. 1986, Micresporangenesis and male gametophyte in some Cucvrbitaceae. Phytomorphology 36: 145-150. Dieringer, G, and R. L. Cabrera. 1994. Sexual selection of anther trichomes and sexual dimorphism in thervittea tindheimeri (Cucurbitaceae: Melothrieae). Amer. J. Bot. 81: 1 1 1-1 18. Eichler, A. W. 1875. Bltithendiagramme. Engelmann, Leipzig. Goffinet, M. C. 1990. Comparative ontogeny of male and female flowers of Cucumis sativus. In D. M. Bates, R, W, Robinson and C. Jeffrey (eds.), Biology and Utllization of the Cucurbitaceae: 288-304. Cornell University Press, Ithaca, Heimlich, L. F. 1927, [[he development and anatomy of the staminate flower of the cucumber. Amer. J. Bot. 5: 227-237.

Hoen, P. 1998. Glessary of Pollen and Spore Terminology, 2nd & rev. ed. Distributed by LPP through http:X/www.bio.uu.nY--palaeelglossaryfindex.htm (downloaded in Dec,, 1998). Imaichi, R. and K. Kobayashi, 1989. F]oral anatomy of Lagenaria siceraria var. microcarpa

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（Cucurbitaceae）with special reference tQ androecium morphQgenesis ． Bul1。 Fac． Agric． − TamagawaUniv ．29： 56 68 （ln Japanese with abstract and figure legends in English ）． and K ． Okamoto．1992． Comparative androecium mo 甲 hogenesis of Sichyos angulatus − and Sechiumedule （Cucurbitaceae）． Bot． Mag ．（Tokyo ）105：539 548， and N ， Uchibori．1992． Androeciu皿 morphogenesis and staminal vasculature of − の ，lindrica（Cucurbitaceae）． Bul1． Fac． Agric． Tamagawa Univ．32： 95 107 （In Japanese with abstr ＆ ct and figure】egends in English）． and 1998 Pollen Ishida， K T ．Hiura． ． fenilityand floweringphenologyin an androdioecious tree， − Fraxinus tanuginosa（Oleaceae）， in Hokkaido， Japan， Int．」． Plant Sci．159：941 947． − Jeffrey， C ，1964． A note on pol豆en morphology in Cucurbitaceae． Kew Bull．17：473 477． ．1980．Areview of the Cucu ゴbitaceae． BotJ ． Linn． Soc．81： 233−247， ，1990．Appendix ： an outline classification of the Cucur itaceae． In D ． M ． Bates ， R ． W ． − Robinson and C ． Jefffey（eds ．）， Biology and Utilizaeion of the Cucurbitaceae：449 463 ． Comell University Press， Ithaca． Judson， J． E 1929， The morphology and vascular anatomy of the pistillate nower of 重he cucumber ． Amer ．1． Bot．16：69−86． Kitamura， S， G ． Murata and M ． Hoh ，1957． Colored IllustraUons of Herbaceous Plants of Japan L

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摘 要

1 ・ 一 2 福 原達 人 秋 本 淳 ： ミヤ マ ニ ガ ウ リ （ウ リ科）の 花部形態 一 雄性 両全 性 異株 の 蔓性 年草 で あ る ミ ヤ マ ニ ガ ウ リ （ウ リ 科 カ ボ チ ャ 亜 科 ミ ヤ マ ニ ガ ウ ・ ー リ連 ）の 花 の 特 徴 ， と くに 雄 し べ 子 房室 の 配 列，維管束走行 ，蜜腺 ，毛 ， フ ェ ノ ロ ジ ・ べ べ つ こ の を 観察 し た 。 両 性 花 雄 花 と も 2 個 の 2 葯 性 雄 し と 】個 の 1 葯 性 雄 し を持 。 よ うな雄 しべ 構成 は ウ リ科 カ ボチ ャ 亜 科 の 多 数 の 分 類 群 に見 られ る が ，そ れ ら で は 2 葯

べ の の て ミ マ ニ ガ ウ リ で は べ に る 性雄 し に 2 本 維 管 束が 入 る に対 し ， ヤ 各 雄 し 入 維管 束 ー は で ろ しべ を つ グ ル プ ス ズ メ ウ リ な ど と 通 す る 他 の 1 本 ， む し 2 葯 性 雄 3 本 持 （ ） 共 。 ウ リ科 の 多 くと 同様 に 葯 と葯 隔 の 境 界 付近 に 大 きな基 部細 胞 を 持 つ 毛 が あ る が ，そ の 形

の の の っ い 状 は他 属 で 既 知 も と異 な り， 球 形 の 細 胞 が 積 み 重 な て る 。 両 性 花 で は 葯 の 裂

い っ い る 開 と柱頭 の 成熟 の あ だ の 時 間差 が 小 さ く， 雌性 期 と雄性 期 は大 き く重 な て 。 両

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・ 性花 雄花 ともカ ッ プ状の 花托 の底 部に蜜 腺 が あ る 。 1 … （ 〒 606−8501 京都 大 学大 学 院人 間環 境 学 研 究科 ［現住 所 ： 〒 606−8157 京都 市 左京区 ・2 ー 乗寺才形 町 7 佐竹方］ 〒 606−8502 京都 大 学 生態 学研 究 セ ン タ ）

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