Dispersal and Distribution of Lecythidaceae and Chrysobalanaceae
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Sonderbd. naturwiss. Ver. Hamburg 163-186 Hamburg 1983 Dispersal and Distribution of Lecythidaceae and Chrysobalanaceae By GHILLEANT. PRANCE & SCOTI A. MORI, New York, U.S.A. With 18 figures and 1 table Sum mar y: The Lecythidaceae and Chrysobalanaceae have both become extremely successful in their colonization of and adaptation to the lowland habitats of the tropics. These families have little variety in their basic fruit type, the Chrysobalanaceae having only a single basic fruit and the Lecythidaceae only two. These have been modified in many ways and have developed a large number of dispersal mechanisms crucial to their adaptability and success. The fruit of the Lecythidaceae (subfamily Lecythidoideae) is either an indehiscent berry like structure or it is a dehiscent circumcissile capsule (pyxidium) which has adapted to many different dispersal vectors. The adaptations of the aril have been particularly important, varying from the fleshy-funicle aril of the bat dispersed genus Lecythis to the aril which forms around the seeds of the wind dispersed genera Cariniana and Couratari. Other dispersal agents include: wa ter, fish, wild pigs, and agoutis. The Chrysobalanaceae are tied to a basic fruit type, a drupe, but have also adapted to many dispersal vectors in the different habitats in which they occur. Dispersal varies from marine in the predominantly insular genus Atuna of Indo nesia and the Pacific, to dispersal by the South American rhea in Parinari ob tusifolia HOOK. f. of Central Brazil, to ichthyochory in species of at least three genera. This variety of dispersal types is discussed in relation to habitat adaptabili ty, distribution in various habitats and the overall geographic distribution of genera and species in both families. Most genera of Lecythidaceae are characte rized by a specific dispersal syndrome but this occurs in many different habi tats. The fruit of most genera of Chrysobalanaceae are distinct, but are less correlated with a particular dispersal type. Examples of probable long-distance dispersal in both families are discussed. However, many disjunct species distributions are better explained by historical changes in vegetation cover. 163 A. Introduction The Lecythidaceae subfamily Lecythidoideae and the Chrysobalana ceae are both extremely successful groups in the lowland tropics in terms of abundance and ecological importance. Both groups are found in a wide range of habitats and have some extremely wide spread species. As would be expected in such well distributed groups there is a wide range of dispersal mechanisms. Although ma ny types of dispersal occur, only three basic types of fruit are involved, two in Lecythidaceae and one in Chrysobalanaceae. These basic fruit types have become modified in many different ways in adaptation to the different vectors present in the lowland tropi cal habitats. Thus, all Chrysobalanaceae have a drupaceous fruit and all Neotropical Lecythidaceae a circumscissile capsule or its indehiscent precursor. Although both families are restricted evo lutionary to these basic fruit types it does not appear to have impaired their ability to utilize a large number of dispersal vec tors. Ac k now 1 e d gem e n t s : We acknowledge with thanks National Science Founda tion grants BMS75-03724 A02; INT75-19282 and INT78-7823341 AOl which have en abled extensive field studies by both authors. We thank Frances MARONCELLI for typing the manuscript, Bobbi ANGELL for preparing the illustrations, and Rupert C. BARNEBY and vicki M. FUNK for critical reading of an earlier draft. B. Fruit types 1. Lecythidaceae All Neotropical Lecythidaceae belong to the subfamily Lecythidoi deae except Asteranthos brasiliensis DESV. which belongs to the predominantly African Napoleonaeoideae (fig. 1A-D). Since our ex perience is with the Neotropical subfamily all further references to the family refer to the subfamily Lecythidoideae and not to the other three subfamilies which were defined in PRANCE & MORI (1979). Three genera of Lecythidaceae have indehiscent fruits, Gustavia, Grias and Couroupita. In these three genera the fruit is large, roundish, and often woody, with a softish or a woody pericarp and the seeds are surrounded by a fleshy pulp (see Couroupita in fig. 3). The seven remaining genera have dehiscent woody pyxidia, ex cept that of Bertholletia excelsa HUMB. & BONPL~, the Brazil nut, which has become secondarily indehiscent (fig. SA-C). The general characteristics and terminology of the Lecythidaceae pyxidium are given in fig. 2 which illustrates species of Lecythis. The pyxi dium is a circumscissile capsule with a dehiscent operculum that encloses compactly organized seeds which are not embedded in a pulp when mature. The variations of the basic fruit are discussed further below in relation to dispersal. 164 I(em. B :· · . ·.· ·~ . ' 0D: ' O · ··· '· ·· _1 ~:'.':": .:.... i.: . • lem. Asteranthos Gustavia ~r,)~' K;U [,i.; , I I" ~h<i ,I::, ,;' ':: ~~~.; II ':~fr···' i'I Grias Allantoma Fig. 1: Fruit and seeds of Lecythidaceae. - A-D. Asteranthos brasiliensis (PRANCE & al. 15481): A. Entire fruit with persistent calyx. - B. Lateral view of seed. - C. Longitudinal section of seed showing tubular embryo embedded in copious endosperm. - D. Cross section of seed. - E-H. Gustavia spp.: E. Fruit of G. superba (MORl 837). - F. Fruit of G. brachycarpa (PlTTlER 5269). - G. Seedling of G. augusta (NEE & MORl 4194). - H. Seed of G. augusta, note the fleshy funicle. - l-K. Allantoma lineata (PRANCE 11618): I. Base of fruit. J. Operculum. - K. Seed with attached funicle-aril. - L-M. Grias neuberthii (BOEKE 2211): L. Entire fruit. - M. Apex of fruit. - N. Seed. 165 II. Chrysobalanaceae The fruit of all Chrysobalanaceae is basically a unilocular or bi locular drupe with an outer mesocarp surrounding a thick or thin endocarp that encloses one or two seeds. The mesocarp is most fre quently soft and fleshy and of variable thickness. In many cases proximal end infracalycine [ zane supra calycine { zane distal end line of aperucular dehiscence B calycine ring line of opercular apercu I or opening dehiscence opercular ring c D ~ E ~"m.", a~.il ~ ~ ......... funicle Fig. 2: Diagramatic representation of fruit characteristics and terminology in Lecythis, a genus with dehiscent fruits. - A. Lateral view of the fruit of L. ampla (operculum removed, MORl 316). - B. Distal view of fruit of L. ampla (operculum removed). - C. Operculum of L. ampla. - D. Operculum of L. pisonis (MORl 399). - E. Seed of L. minor (MORl 423). it is sweet, and consequently edible. In some, for example Atuna (fig. 7A), the mesocarp is hard and woody. The endocarp is usually indehiscent and on germination gradually breaks up. The endocarp has become dehiscent in some genera, either by longitudinal lines of dehiscence as in Chrysobalanus (fig. 8) and most species of Hirtella, or by lateral plates as in Grangeria, Maranthes and Para stemon (fig. 17), or by basal stoppers or obturamenta as in Neo carya and Parinari. 166 C. Dispersal mechanisms I. Lecythidaceae 1. Indehiscent fruit As pointed out above, the fruits of only three genera of Lecythi doideae are indehiscent. These are all genera which we consider to be relatively primitive. It is interesting to note that all Old World Lecythidaceae of the other three subfamilies have indehis cent fruits, indicating that, since indehiscence is a primitive character, the family originated in the Old World. This conclusion is correlated with many floral characters and is not based on fruit dehiscence type alone. The two genera, Gustavia and Grias, which we consider most primiti ve in both floral and fruit structure, have indehiscent fruit (fig. 1: E-H, L-M). Those of both genera mature on the trees and drop directly to the ground or water as the case may be. Those of Gusta via and Grias differ from those of all other Neotropical Lecythi daceae in that they are softish. The mesocarp is easily bitten in to by animals. The entire fruit together with the numerous seeds is the initial unit of dispersal as it falls from the tree (baro chory). However, in each species where observations have been made, secondary dispersal occurs, most frequently by animals. For exam ple, the orange mesocarps of Gustavia superba (KUNTH) BERG and G. grandibracteata CROAT & MaRl are eaten by mammals. Once the exo carp has broken open, the orange mesocarp attracts animals and seeds are dispersed as the fruits are carried to eating places and the seeds themselves are often scatter hoarded. Gustavia augusta L. is a riverine species whose fruits usually fall into the water. Not only are they rafted by water, but they are eaten by fish and have been found in their digestive tract (HONDA, 1974°; PRANCE, pers. obs.). This is one of many Amazon sp~cies in which ichthyo chory is important (see GOULDING, 1980). Although most species of Gustavia and Grias have a soft fruit, a few species such as Grias cauliflora L. have a harqer exocarp. Grias cauliflora is a riverine species and as early as 1917 GUPPY reported that the entire fruits are buoyant, although the seeds alone sink. He observed that the fruits f Loa't; readily beside the banks of rivers on which it grows. They can float for months and germinate in river drifts. They are, however, killed by sea water, although the seeds are frequently found amongst beach drift. G~ias cauliflora is common in Central America from Belize to Panama, but also occurs in Jamaica, which may indicate that long distance dis persal over sea water occurred successfully at least once. However, the fruits of G. cauliflora, do not differ SUbstantially from those of the other species of Grias and Gustavia. The exocarp of G. cauliflora does not differ from that of its animal dispersed congeners. This species is riverine and also primarily animal-dis persed. Its secondary dispersal by water has drawn more attention from previous workers because of its occurrence on Jamaica.