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Malayan Nature Joumal200l, 55 (1 & 2): 133 ~ 146

The Significance of Gynoecium and Fruit and Seed Characters for the Classification of the Rubiaceae

CHRISTIAN(PUFF1

Abstract: This paper attempts to give a survey of the highly diverse situation found in the gynoecium

(especially ovary) of the Rubiaceae (multi-, pluri-, pauci- and uniovulate locules; reduction of ovules and septa in the course of development, etc.). The changes that can take place after fertilisation (i.e., during fruit and seed development) are discussed using selected examples . An overview of the many diverse types of fruits and seeds of the Rubiaceae is presented. In addition, the paper surveys the diaspores (dispersal units) found in the family and correlates them with the morphological-anatomical

situation. Finally, selected discrepancies between "traditional" classification systems of the Rubiaceae and recent cladistic analyses are discussed. While DNA analyses and cladistic studies are undoubtedly needed and useful, it is apparent that detailed (comparative) morphological-anatomical studies of gynoecium, fruits and seeds can significantly contribute to the solution of "problem cases" and should not be neglected, Future cladistic :work should, therefore, more generously include such data.

INTRODUCTION

The Rubiaceae, with approximately 11 ,000 species and more than 630 genera (Mabberley 1987, Robbrecht 1988), is one of the five largest families of angiosperms. Although centred in the tropics and subtropics and essentially woody, the family also extends to temperate regions and exhibits a wide array of growth forms, with some tribes having herbaceous, and even annual members. Not surprisingly, floral, fruit and seed characters also show considerable diversity.

One of the main aims of this paper is to give a survey of the female reproductive structures, concentrating on the ovary. Moreover, it will describe changes taking place after fertilisation, and also survey fruit and. seed characters, correlating them with ecological aspects ( diaspores-dispersal units-and their mode of dispersal vs. morphological-anatomical fruit and seed structure). Finally, it will also discuss the significance of gynoecium, fruit and seed structure for the classification of the family.

1 Institute of Botany, University of Vienna, Rennweg 14, A-1 030 Vienna, Australia

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THE CHARACTERS2

Gynoecium

The basic type of Rubiaceae flower is five-merous, sympetalous and has an inferior ovary. With regard to the gynoecium, it is now quite safe to assume that, in spite of the five-merosity of the other floral parts, the basic situation is a bicarpellate gynoecium (this appears to be confirmed by cladistic analyses, e.g. Bremer et al. 1995, Bremer 1996b). The presence of two carpels, in fact, predominates in the family, occurring in tribes of all recognised subfamilies (Robbrecht 1988: Fig. 34).

While numerous tribes are characterised by a strictly bicarpellate situation, others show increases in carpel numbers.

Several tribes, such as Psychotrieae, show an increase from two to five. In others, the number may be even further increased (to over 10, in, for example, the Vanguiereae). The Urophylleae are perhaps the tribe with the highest range of variation in carpel number: (3-)4 to 8( -16) (Buchner 1995).

Increase in carpel number is sometimes even recorded within genera, e.g., in the predominantly 4-5-carpellate genus Lasianthus (PSY.P.), carpel number may be increased to over 10 ..

The genus Timonius (GUE.) represents a very exceptional and-in Rubiaceae -unique situation. Ovaries may contain up to 150 locules, each with a solitary ovule (and, subsequently, drupes with the same number of pyrenes!). This comes about-as in Punica (Punicaceae) or the Navel Orange-by a secondary increase in the number of carpels, caused by secondary formation of successive whorls (Martinello 1992).

On the other hand, there are also reductions of the basic bicarpellate situation: Theligonum (THE.) is characterised by having a "1-locular ovary, with a s.ingle basal ovule" (Robbrecht 1988); recent, detailed investigations, however, show that the ovary is basically bilocular, but the incomplete septum is overarched by the only ovule (Rutishauser et al. 1998). While the wind-pollinated African and Madagascan Anthospermeae-Anthosperminae basically are bicarpellate, one of the two carpels is infertile, variously reduced and modified (and only 1 stigma present) in all but one species of the South-western Cape genus Carpacoce; similar reductions are also documented for two of the 39 species of Anthospermum (Puff 1986).

' .

Ovary position. Although the overwhelming majority of Rubiaceae have inferior ovaries, some-notably Gaertnera and Pagamea (PSY.)-are cited as having (semi-) superior ovaries. In a detailed investigation of the paleotropical Gaertnera, Igersheim et al. (1994), however, prove that the ovary only becomes secondarily superior in the course of floral development. They suggest that its neotropical counterpart, Pagamea, exhibits the same situation and speculate that "half-inferior" ovaries such as those of some Hedyotideae taxa (cf. Jovet 1941) are basically inferior and represent

2 The abbreviations for tribes and subtribes used throughout the text follow Robbrecht (1988). The inclusion of the Hedyotideae, and of genera of the Knoxieae, in the Spermacoceae (Bremer 1996a) is not followed here.

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only a variation of the general situation.

Fused ovaries. In a number of Rubiaceae, adjacent ovaries ·of one and the same flower are united by tissue fusion from the pre-anthesis stage onwards. In the simplest case, it is two fused ovaries (Mitchella, MIT.), in other cases it is several to many (e.g. Morinda, MOR., or Rennellia, PRI.). Ovary fusion is not tribe-specific; in the Naucleeae, for example, there are taxa with both fused and free ovaries, although the basic inflorescence type is the sa~e in all of them (Ridsdale 1978).

As the presence or absence of ovary fusion determines which kind of dispersal unit will develop (infructescences, if ovaries are fused; see below), it is a feature to be looked at closely.

True, false, complete and incomplete septa. The normal or "typical" situation is that septa completely separate locules, whereby the septum marks the border between two adjacent carpels. In some (basioally bicarpellate) taxa, however, the septum never is fully continuous (it is "incomplete" in that it leaves a gap between two locules). An example is Faramea (COU.), where in early floral stages the septum is only visible at the base of the ovary. In Theligonum, too, the septum is incomplete (see also reduction of carpels, above).

False septa of certain Rubiaceae are outgrowths of the carpel wall which extend through the locule towards the centre of the ovary. They either are restricted in their growth (never actually reaching the centre; "incomplete"), or they actually completely subdivide a locule because they come in touch with the centre. In Strumpfia (INC.SED.), for example, cross sections of ovaries (from top to bottom), first sho~ a seemingly 4-locular ovary, then the true septum and two false septa retracting from the centre, and finally a bicarpellate ovary, without any trace of false septa at all (Igersheim 1993). Both, the African Pauridiantheae and the Asiatic Urophylleae are characterised by ovaries with false septa. In both, the false septa are usually only continuous in the apical part of the ovaries but (largely) disappear further below (Bangoura 1993, Buchner 1995). Due to the presence of false septa, the ovary structure of, for example, Praravinia (URO.; with up to 16 carpels) may become highly complicated.

Also the presence of large placentas, extending all the way to the carpel walls, may mimic the presence of false septa. In Morinda, with bicarpellate ovaries and two ovules per locules, the placentas are so massive and extensive that they divide each locule into two halves (thus giving the impression that the ovaries are 4-locular and only contain one ovule per locule) (Igersheim and Robbrecht 1993).

Placentation. The ~ubiaceae are basically characterised by an axile placenta. There are, however, transitions from axile to parietal, and truly parietal placentas (especially in the Gardenieae; Robbre~ht and Puff 1986). Moreover, some tal(a (e.g. those with incomplete "true" septa, see above), show a placentation that at least approaches basal placentation. -

The insertion and shape of the placentas are highly variable. They may be attached to the entire septum or, in the other extreme, to only a very small portion

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of it. Their shape ranges from small to very large, they may be variously divided, ± sessile or stalked (see Robbrecht 1988 for details).

Noteworthy are proliferating placentas (particularly prominent in genera of the Gardenieae). Placentas start growing around the ovules, eventually immersing ­them. This process starts at (or even before) an thesis and continues during fruit development (finally, the seeds are totally immersed in a fleshy pulp) (e.g. Euclinia; Halle 1967, Fig. 37).

Ovules. Presumably the basic situation in the Rubiaceae is a large placenta bearing numerous ovules. The latter are mostly anatropous (or hemi-anatropous), but a trend to camp:Ylotropous ovules is noticeable (recorded for various taxa of diverse alliances but apparently particularly common in PAV.; de Block 1995).

Various tribes are characterised by consistently pluriovulate placentas, but for several others reduction series are documented. In Tricalysia (GAR.D.), for example, the ovaries are multi- to two- and, in a few species, even consistently uniovulate (Robbrecht 1979, 1987).

On the other hand, a large number of tribes is almost exclusively defined by having uniovulate locules. In this group, two very clear-cut categories can be distinguished: (a) ovule (and placenta) inserted near or at the base of the septum, and the micropyle of the erect ovule points down- and outward (away from the septum)( e.g. Paederia, PAE., Svoma 1991); (b) ovule (and placenta) inserted near or at the top of the septum, and the micropyle of the pendulous ovule points up- and inward (towards the septum) (e.g. Dichilanthe, GUE., Puff et al. 1996). Exceptions are known for neither (a) nor (b).

The monotypic mangrove genus Scyphiphora is quite unusual with regard to the arrangement of the two ovules per locule: one is ascending, the other descending; both are anatropous, and in each the micropyle faces the septum (Puff ar1d Rohrhofer 1993).

Changes Taking Place during Anthesis and after Fertilisation

Abortion of ovules and seeds. Abortion can start even during anthesis. An example in point is Faramea (COU.) which has been studied in detail (Puff unpublished): soon, one of the two ovules becomes larger and curves around the second which remains small (it can do so because the genus has an incomplete "true" septum, which leaves a gap in the upper part of the ovary). Eventually, the aborted ovule becomes crushed and is almost fully enveloped by the fertile one. The mature fruit of Faramea, consequently, has only a solitary seed attached to its base and seems to be unilocular (because of the incomplete septum). In the allied genus Coussarea, the situation is basically similar, although the seemingly unilocular, one-seeded fruits look quite different (elongated, versus horizontally compressed in Faramea). This comes about because of the expansion of the fertile ovule in a vertical rather than horizontal plane. In the Craterispermeae (Craterispermum only), too, fruits are always one-seeded, although each of the two locules of the ovary originally contained an apically _inserted, pendulous ovule. The way the one-seededness comes about is, however, quite different to the Coussareae (see Igersheim 1992).

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Obligatory ovule abortion as in the examples given above appears to be rare. In several genera, there is, however, a rather clear trend towards abortion. In the Vanguerieae, for example, fruits of Keetia rather frequently are one-seeded by abortion. Such one~seeded fruits can normally be spotted by their shape: The fertile seed tends to grow around the aborted one (and in doing so causes a deformation of the septum); the result is a fruit that has become curved and that shows the persistent calyx in a somewhat displaced, i.e. more lateral, position (Igersheim 1989).

Seed abortion (and crushing of the locule that contains the aborted seed) is also not uncommon in taxa with infructescences. In Rennellia elliptica, for example, an infructescence (which theoretically could contain six seeds as it is made up of three fused gynoecia, each with two uniovulate locules) may only have a solitary fertile seed. The presence or absence of aborted seeds, moreover, influences the shape of the fertile seed( s) (see Igersheim ahd Robbrecht 1993 for details).

Drastic shape change in the transition from ovule to seed stage. This is often particularly conspicuous in taxa which develop winged seeds. In bud· stage, ovules may still be of "typical" ± ellipsoidal shape, offering hardly any clue that they are going to develop into winged seeds; at anthesis a slight elongation of the ovules, indicating the start of the wing formation, may become noticeable (e.g. Danais, CIN./HED.; Buchner and Puff 1993). In other taxa producing winged seeds, characteristic wing-like elongation of the chalaza! region of the ovule (accompanied by lateral compression of the entire ovule) may, however, already be observable before the onset of anthesis (e.g. Mussaendopsis, COP.; Puff and Igersheim 1994).

In Hillia (HIL. orCIN.), a genus producing seeds with tufts of hairs attached to one end (the hairs being several times as long as the actual seeds), ovules in bud stage, although still of ovoidal shape, already show _protuberances (the first stages of hair formation). At anthesis, ovules become laterally compressed and hair formation becomes more obvious. It is, however, only during fruit development (after fertilisation) that the hairs start elongating drastically (Puff and Buchner 1998a).

Changes from ovary wall to fruit wall. The ovary wall, observed at anthesis, usually gives a good clue as to what the wall of the mature fruit will look like. Frequently, the ovary wall will show a differentiation into discrete tissue layers which largely correspond to exo-, meso- and endocarp of the fruit wall. Obviously, the degree by which the different tissue layers thicken and expand in the transition to the fruit stage will be highly variable from taxon to taxon.

There are also cases where the transition of ovary wall into fruit wall is accompanied by drastic changes. An example is Scyphiphora (GAR.D.), were the changes are causally connected to the mode of dispersal of the fruits (the genus occurs in mangroves and produces fruits dispersed by sea currents; see also Dispersal and Dispersal Units, below) (Puff and Rohrhofer 1993).

Fruits and Seeds

The basic type of fruit of the Rubiaceae appears to be a many-seeded capsule (rather

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than an indehiscent fruit). Capsules, indeed, are common in the family, occurring in many tribes and in

taxa with diverse growth forms (trees -> herbs). Capsules either split open loculicidally or septicidally. Even in obviously closely related alliances, the mode of dehiscence can vary between genera (e,g. in the Danais - Schismatoclada -Payera complex, CIN./HED., the first and last have loculicidally, and the second septicidally dehiscing capsules; Buchner and Puff 1993). Also combinations of both modes occur (for example, capsules at first splitting open loculicidally, and at length also septicidally, at least at the top).

In capsules, the fruit wall is uniformly hard, although the innermost layer is often anatomically slightly different, consisting of solid sclerenchyma. In contrast, drupes, another extremely frequent fruit type in Rubiaceae, are characterised by a skin-like, thin exocarp, a thick, fleshy (often watery) mesocarp and a sclerenchymatic endocarp of varying thickness. The latter forms the "stone" or pyrene which encloses the seed(s). Normally, stones within a fruit are free from each other (their number corresponding to the number of carpels present), but sometimes, endocarps of all neighbouring carpels become united, thus forming a plurilocular stone (e.g. Guettarda speciosa, GUE., see also Dispersal and Dispersal Units, below). Hedyotis (HED.) appears to be the only genus in which there are transitions from capsular to drupaceous fruits: in a few species (e.g. H. philippinensis), fruits no longer dehisce, the mesocarp becomes more or less thick and fleshy, and the endocarp is distinctly sclerenchymatic; each stone contains numerous seeds (normally, pyrenes contain a solitary seed!).

Rubiaceous fruits, in literature often referred to as "berries", are in fact often drupes because they do have a sclerenchymatic endocarp (which, however, may only be a few cell layers thick); the descriptive term "berry-like" fruits would be more appropriate. "True" berries (defined as having a thick, fleshy fruit wall but no hard endocarp) are relatively more uncommon (e.g. Sabicea, ISE., Puff et al. 1998).

Equally uncommon are "true" nuts (indehiscent fruits with a continuously hard, sclerenchymatic endocarp). Nut-like fruits are often "modified" drupes, in which the parenchymatic mesocarp becomes hard and dry at maturity. Nematostylis (ALB.) and the indehiscent fruited Alberta magna (ALB.) are examples of taxa which appear to approach "true" nuts (Puff et al. 1984).

In a considerable number of taxa, the fruits break into mericarps or partial fruits. Each mericarp corresponds to a carpel and normally contains a single seed. This feature is not confined to certain alliances and occurs in both woody groups (e.g. Alberta, ALB.) and herbaceous groups (e.g. Galium, RUB.). It is not always genus-specific (in the first mentioned example, one species has indehiscent fruits; Puff et al. 1984 ). Typically, the mericarps themselves are indehiscent. Occasionally, however, the mericarps themselves dehisce to release the seeds (e.g. Spermacoce spp., SPE.) Various "special" types of fruits, representing modifications of the types described above occur. Amongst these are:

Lid capsules, where the roof of the fruit comes off like a lid (e.g. the apical operculum in Argostemma, ARG., or Pseudopyxis, PAE.; Sridith 1997, Puff 1990), or where the fruit is circumscissile around its middle (e.g. Mitracarpus, SPE.; Verdcourt 1976, fig. 55).

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Valvate capsules, where each valve corresponds to a respective carpel portion. An example is Leptodermis (PAE.) (Puff 1990). In this genus, however, the capsule does not release the seeds alone (as is otherwise typical of valve capsules) but seeds enclosed in a "mesh" formed by the anastomosing, hardened vascularization of the fruit wall.

In Deppea (syn. Schenckia; see Lorence and Dwyer 1988), the fruit wall at length largely disintegrates, leaving behind a skeleton formed by the persistent vascular supply which serves as a kind of basket.

Yet another example where the persistent vascular supply plays a certain role is the highly complicated fruit of Paederia (see Igersheim and Puff 1991 and Svoma et al. 1991 for details).

Finally, the occurrence of infructescences3 needs mentioning. The term applies to situations where two or more ovaries are united by tissue fusi,on from the pre­anthesis stage onwards. The best known example is Morinda (MOR.), but various other alliances, notably the Prismatomerideae, also contain taxa with infructescences (cf. Igersheim and Robbrecht 1993).

The term should not be used (as is often done in literature) for taxa in which (ovaries and) fruits, usually in a more or less globose arrangement, are merely in close proximity to each other but not fused. An example in point would be Schradera (syn. Lucinaea) (cf. Puff et al. 1993); because of the superficial resemblance to Morinda, with "true" infructescences, the type species has originally been described as Morinda polysperma.

Table 1 summarises the types of fruits in Rubiaceae and also includes information on diaspores (dispersal units).

Seeds

Seeds of Rubiaceae are exotestal (sensu Comer 1976), and the seed coat or exotesta (having arisen from to the integument- epidermis of ovules in the flowering stage) serves as a prot~ction layer for the seed. The layers below (endotesta) are normally crushed in mature seeds. Only a few taxa are known in which the endotesta of ripe seeds is at least partially intact (e.g. Schradera or Lecananthus, Puff et al. 1993, Puff and Buchner 1998b ).

In most taxa the exotesta has prominent (local) secondary thickenings which are highly variable in their micromorphology and can be of systematic relevance. See, for example, Robbrecht and Puff (1986) who give an overview of the many types of thickenings in the Gardenieae and allied tribes.

Only a few taxa are known in which the exotesta is not a continuous cell layer but instead is comprised of isolated cells on the surface of the seeds (in these cases the originally continuous exotesta does not follow the dil<ttation growth of the seed and is, subsequently, ripped into pieces). For a detailed documentation in Craterispermum see Igersheim (1992); another well known example is Coffea.

Rubiaceous seeds always·contain endosperm, but the amount of endosperm

3 The tenn "syncarp" should be avoided; see lgersheim and Robbrecht(l993: footnote 2).

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Table 1. '!ypes of fruits and diaspores (D; Dispersal Units) in Rubiaceae.

A. Solitary Fruits

AI. Fruits opening in various ways [D = seed; or: endocarp + enclosed seed] Ala. Capsules

loculicidal dehiscence septicidal dehiscence

- combination of both Alb. Lid capsules (operculate dehiscence) Ale. Capsules with valves (valvate dehiscence) Ald. special: fruit wall largely disintegrates, leaving behind a skeleton formed by the persistent

vascular supply

A2. Fruits breaking into one-seeded units [D =partial fruit (mericarp)] Typically, mericarps are indehiscent. Exception: mericarps, which at length break open [meaning D = seed; a kind of "dual mechanism"]

A3. Fruits not opening at maturity [D =fruit] A3a. entire fruit wall fleshy: berries A3b. entire fruit wall dry and hard: nuts A3c. Fruit wall fleshy (mesocarp) and hard (endocarp): drupes Endocarp plus seed(s) (="stone"

or pyrene) either "free" or fused ("plurilocular stones")

B. Infructescences [D =all fruits of an inflorescence] In the strict sense, the term only refers to situations were neighbouring (gynoecia and) fruits are joined by tissue fusion, and NOT to (often globose) inflorescences in which the many fruits are merely in close proximity!

tissue varies from copious to just a few tissue layers. There tends to be a negative correlation between the amount of endosperm and embryo size (large embryos­little endosperm and vice versa).

Numerous alliances have taxa with winged seeds, whereby the size and shape of the wings is highly variable (circular, bi- or tripolar, unilateral; margins more or less smooth or fringed). The wings always seem to be exotesta outgrowths (usually consisting of only two--"upper" and "lower"-exotesta layers and mostly without endosperm in between; e.g. Danais and relatives, Buchner and Puff 1993).

Comose or "plumed" seeds occur in Hillia (HIL. orCIN.). Puff and Buchner (1998a) present a detailed study of their origin and structure and state that the resemblance to taxa of Apocynaceae and Asclepiadaceae with hair tuft seeds is merely superficial4

•

Ruminate seeds also occur in Rubiaceae, but this phenomenon is rare in the family (only known from 14 genera). For a full documentation of the ruminate seeds of Rutidea (PAV.) and their development see de Block (1995).

4 (a) Recent cladistic analyses suggest that Asclepiadaceae are to be merged with Apocynaceae (Struwe et al. 1994). (b) Both Rubiaceae and Apocynaceae (incl. Asclepiadaceae) belong to the same order, i.e. Gentianales. '

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Dispersal and Dispersal Units

The majority of Rubiaceae diaspores are undoubtedly dispersed by wind or animals (although it is not to be overlooked that there is presumably a large number of Rubiaceae taxa whose diaspore dispersal is quite unspecific). Table 2, nevertheless, shows that a very wide range of different diaspores is present in the family.

The largest (morphological) diversity is found amongst anemochorous diaspores. Small to minute and winged seeds ( 1.1. and 1.2. in Table 2) are the most common diaspores, with all others being uncommon to rare. Seeds with an apical tuft of hairs are only present in the (largely) epiphytic Hillia (Puff and Buchner 1998a). Winged mericarps occur, for example, in species of Knoxia (KNO.) (Puff and Robbrecht 1989), or in Nenax spp. (ANT.A.) (Puff 1986). Winged endocarp plus enclosed seed (the latter also held in place by the persistent vascular supply of the fruit) refers to the diaspores characteristic for two subgenera of Paederia ( cf. Igersheim and Puff 1991). Either entire (indehiscent) fruits or mericarps with enlarged persistent calyx lobes serving as flying apparatus occur in several alliances; both occur together in the genus Alberta (although not in the same species; Puff et al. 1984). Gaillonia anthospermioides (syn. Crocyllis a.; see Thulin 1998) and Anthospermum littoreum are examples for taxa whose fruits or mericarps, beset with long, stiff hairs, are rolled about by wind (Puff and Mantell 1982, Puff 1986). The most unusual rubiaceous anemochorous diaspores, mimicking those of dipterocarps, are found in Dichilanthe (GUE.); they are comprised of the entire inflorescence in fruiting stage plus a pair of enlarged bracts immediately below it (Puff et al. 1996).

Zoochorous diaspores are much less diverse. Endozoochorous diaspores (2.1. in Table 2), are by far the most common; drupes, "berry-like" fruits, "true" berries and syncarps form most of the diaspores.

Ornithochorus diaspores tend to be rather small, but normally attractively coloured (bright red, pink, yellow, etc.) (cf. Halle 1974). Diaspores eaten by larger mammals are often quite large; a well-known example being the African Gardenia species, whose large fruits are a favourite source of food for elephants (several pers. obs.).

Epizoochorous diaspores (mericarps with hooked hairs) appear to be restricted to the herbaceous Rubieae, especially Galium spp.

Myrmecochorous diaspores (seeds with elaiosome), too, are known only from herbaceous Rubiaceae. The presence of a ring-like elaiosome in Theligonum (THE.) has recently been documented in etail (Rutishauser et al. 1988). The "dependances charnues" on the seeds of certain Spermacoce (syn. Borreria) spp. (SPE.) (Miege and Assemien 1962), being fleshy appendages which represent parts of the placenta, probably, too, refer to elaiosomes.

Hydrochorous diaspores are few and morphologically diverse. Two examples for (long-distance) dispersalby sea currents which have been known for a long time (see Robbrecht 1988) are (a) the infructescences of Morinda (MOR.) and (b) the modified drupes of Guettarda speciosa (GUE). In both cases, the seeds are enclosed in sclerenchymatic endocarps which effectively protect them from sea water and its adverse effects. THe Asiatic mangrove shrub or tree Scyphiphora

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Table 2. Correlation between DISPERSAL METHOD and kind of DIASPORES mentioned in the previous table.

1. Dispersal by wind (Anemochory):

1.1. D =small seeds to minute seeds(± dust seeds) [capsular fruits] 1.2. D =winged seeds (circular, bi- or tripolar wings, etc.) [capsular fruits] 1.3. D =seeds with tuft of hairs ("plumed" seeds) [capsular fruits] 1.4. D = winged mericarps 1.5. D =winged endocarp plus enclosed seed 1.6. D =fruit plus enlarged persistent calyx lobes (serving a flying apparatus) 1.7. D = mericarps plus persistent enlarged calyx lobes 1.8. D =fruits with long hairs (desert/savanna "rollers" or "tumblers") 1.9. D =whole inflorescence in fruiting stage plus pair of enlarged bracts immediately below

2. Dispersal by animals (Zoochory):

2.1. Endozoochory: -Larger mammals (e.g. elephants, monkeys, etc.) [indehiscent fruits] - Ornithochory (bird dispersal)

D =fruit (drupe, berry), or D = infructescence

2.2. Epizoochory: D = mericarp (+hooked hairs)

2.3. Myrmecochory:

D = seed plus elaiosome

3. Dispersal by water (Hydrochory):

"Floaters" (sea currents or fresh water): D = fruit (modified drupe) D = infructescence D =seed

4. Rain drops-(splash dispersal):

D =seed [erect, cup-like capsule; sometimes combined with false vivipary: germination within capsule]

5. Geocarpy:

D =fruit (mericarps)

Unspecific, abiotic dispersal:

D =seed [many capsules; seeds merely falling out]

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(GAR.D), again with modified drupes which are morphologically-anatomically adapted to dispersal by sea currents (details in Puff and Rohrhofer 1993) is a third example. So far, there is only a single known example of floating seeds: Abbiw ( 1988) pointed out that, in contrast to other Nauclea spp. tested, only Nauclea pobeguinii (a tree occurring in marshes and flooded forest) has seeds that float on the water surface. Dichilanthe, known for its unusual anemochorous diaspores (see above), appears to follow a "double strategy": once dispersed by wind and having landed in running water, the diaspores are capable of floating (thanks to anatomical adaptations of the individual modified drupes; see Puff et al. 1996 for details).

Dispersal by rain drops (or drops of falling water in general), well known from other tropical forest floor herbs such as Sonerila or Phyllagathis, Melastomataceae), probably only occurs in Argostemma (ARG.) and Ophiorrhiza (OPH.). At full maturity, the apical lids of the fruits have fallen off, and the fruits themselves are held in a more-or-less vertical position. They are thus cup-like structures ("splash cups") in whose interior are the (normally) numerous seeds. The seeds are then ejaculated ("splashed out") by drops of (rain) water. Ophiorrhiza is basically similar, and-as in Argostemma-the fruits move into a ± vertical position when they hecome fully mature. The fruits, however, are "normal" (although laterally compressed) capsules without lids. Moreover, in Ophiorrhiza, the seeds often start germinating while still in the fruit ("false" vivipary; cf. Tan and Rao 1981). This phenomenon was never observed in Argostemma.

According to our present state of knowledge, the only known and documented case of geocarpy in the Rubiaceae is found in Galium ankaratrense (RUB.), a species endemic to a central Madagascan mountain range (Kiehn and Puff 1988).

DISCUSSION

In Schumann's (1891) treatment of the Rubiaceae (taken over, with only relatively few modifications·, from Hooker 1873 ), only two subfamilies are recognised, solely based on the number of ovules present (the Coffeoideae with a solitary ovule per locule, and the Cinchonoideae with more than one ovule per locule ). This obviously highly artificial classification was heavily criticised and rejected by later authors (it should be kept in mind, however, that Schumann's work is the most recent world­wide treatment of the family at the generic Level and contains a wealth of highly useful information).

Later classifications, e.g. Bremekamp ( 1966), recognising eight subfamilies, empnasised other character states, and it became clear that ovule number cannot be used for the main divisions of the family.

In 1988 Robbrecht came up withan updated classification, stating that "it is possible to arrive at a satisfactory delimitation offour subfamilies based on distinct character combinations and trends." In his work, each of the subf!lmilies, tribes and subtribes belonging to them are precisely defined. It transpires that gynoecium characters (e.g. ovule number, type of placentation, etc.) as well as fruit and seed characteristics do play an important role, although they are usually not the only characters defining a given taxonomic entity.

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The understanding of both structure and development of the gynoecium, based on anatomical work, as well as an understanding of the changes taking place from ovary to fruit (and ovule to seed) stage are highly important. Several of the examples given in the previous chapters could significantly contribute to the clarification of the taxonomic position of taxa.

Comparisons of detailed gynoecium structure will, in most cases, allow certain conclusions on relationships. Anatomical data will, for example, most likely P!ovide proof for the coherence of taxa showing a reduction series from multiovulate to pluriovulate and pauciovulate. It is thus strongly suggested that more studies of this detailed nature are undertaken in the future.

While the value of cladistic analyses is certainly not disputed, one must be careful of oversimplification of character states in data matrices, as the results most likely will be distorted. As can be concluded from the above, the situation in the Rubiaceae is complex, and many modifications are known, and these should be taken into consideration. The simplified characterisation of fruit types in Bremer and Eriksson (1992), for example, is not compatible with that given in the present paper. Merely using "1-, 2- or 3-locular" as character states for the ovary (in the combined and separate analyses of morphological and molecular data in the Rubiaceae; Bremer 1996b ), is hardly satisfactory.

Neither does it seem to be particularly useful to suggest major realignments based solely on cladistic analyses of molecular data (e.g. inclusion of the Hedyotideae and genera of the Knoxieae in the tribe Spermacoceae; Bremer 1996a) without having supporting evidence from detailed investigations of, for example, gynoecium, fruit and seed characters.

That said, recent cladistic analyses of Rubiaceae do consistently show one very noteworthy situation that needs further consideration: one of the four subfamilies recognised by Robbrecht ( 1988), the Antirheoideae, is likely to be polyphyletic (Bremer 1996b and literature cited therein). One of the main characteristics of the subfamily is the presence of a solitary pendulous ovule per carpel which is attached near the top of the septum. In view of the cladistic analysis it seems clear that this very conspicuous gynoecium character has been overemphasised, does not reflect a natural relationship and appears to represent the endpoint of a reduction series which has occurred several times in different alliances. From the point of gynoecium morphology and anatomy, however, there is no evidence whatsoever corroborating this. The Antirheoideae ovary with its solitary pendulous ovules seems to stand "isolated," not linking up with pluri- and multiovulate ovaries. Theoretically, it is possible to establish a relationship to taxa with a solitary basal, erect ovule per locule (such as in PSY.), but this is certainly not supported by other character states. Every effort should be undertaken to solve this problem.

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