Abstract
SummaryFruit morphology and the anatomical structure of the pericarp, fruiting perianth, and seed coat were studied in 15 species of Poikilospermum, a genus whose position within the Urticaceae has long been controversial. Possible evolutionary trends of their transformation are suggested for both subgenera; plesiomorphies were found in P. oblongifolium and P. scabrinervium. Structural peculiarities of the fruit connected with its ejection out of the tubular perianth are discussed. The archaism of the fruit in Poikilospermum is revealed, indicated, as in Boehmeria, by the presence of the rudiment of an aborted carpel in the form of a large two-lobed rib. Using carpological anatomical characters, the species studied are classified into informal groups, such characters being able to pull the species within the subgenera into rough groupings where gross morphology has been unable to do so. It is shown that heterobathmy may be strongly associated with the genus Poikilospermum. Each subgenus has its own set of primitive carpological characters: in subgenus Poikilospermum the absence of a fruiting perianth which encases the fruit, and also of capitate inflorescences with swollen receptacles; in subgenus Ligulistigma remnant rudiment of the second carpel and ovary loculus, as well as a primitive, less simplified seed coat. Though the position of Poikilospermum as indicated by molecular data is within Urera, our results suggest that Dendrocnide (the only genus of the Urticeae that has a pyrenarium fruit type) may be closest to Poikilospermum, although the pericarp structure and dissemination behaviour in Poikilospermum are more specialised than those exhibited by Dendrocnide. Seed coat structure is also shown to exhibit traits seen in Moraceae.
Highlights
The genus Poikilospermum Zipp. ex Miq., found in Indo-Malesian regions of the Old World tropics, numbers approximately 20 species (Chew 1963)
Correlation of informal groupings based on fruit structure with gross morphology and geographical distribution and some evolutionary observations (A) Subgenus Poikilospermum Group 1
Poikilospermum acuminatum The mechanism of tubercle formation in Poikilospermum acuminatum is unique within the whole genus Poikilospermum
Summary
The genus Poikilospermum Zipp. ex Miq., found in Indo-Malesian regions of the Old World tropics, numbers approximately 20 species (Chew 1963). Ex Miq., found in Indo-Malesian regions of the Old World tropics, numbers approximately 20 species (Chew 1963). A combination of characters from both Urticaceae and Moraceae has been noted in Poikilospermum (for instance, Chew 1963; Grudzinskaya 1980). Moraceous traits are found mainly in the structure of vegetative organs, whereas Urticaceous ones are found in reproductive organs. Among the reproductive parts there are characters in accord with Moraceae: erect filaments of stamens in bud (in subgenus Ligulistigma), swollen peduncular receptacles similar to those of Artocarpus and mucilage localisation in the mesocarp instead of the exocarp (Berg 1977, 1978; Kravtsova 1995).
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