A REVISION OF THE GENUS HELIOCARPUS L.1 KO KO LAY INTRODUCTION Heliocarpus has received considerable attention from plant systematists prob-ably because of the perplexing variation found in the genus and because of the few constant characters of taxonomic value. Furthermore, in the herbarium, the speci-mens are either in fruit or in flower, never both; and when in flower are either hermaphrodite or pistillate. Thus, assigning them to any particular species be-comes extremely difficult. Despite a recent taxonomic study of the genus,' there is still considerable confusion regarding many species both in the literature and in the herbarium. More than fifty species and varieties have been named thus far, and with the prevalent vagueness in the concept of speciation, there appears super-ficially to be but two alternatives: either to split the genus into innumerable in-distinct and undefinable "species" or to lump them indiscriminately into few cate-gories of scarcely greater reality. In my study of the genus an attempt has been made to escape this dilemma byclarifying the concept of speciation. However, as this study has been confinedentirely to herbarium specimens which represent only very small portions of thewoody plants, no definite idea or suggestion as to the individual variations ofsingle plants has been obtained. I bave been fortunate enough in being able tostudy specimens from nearly all the major herbaria both in the United States andin Europe. The standard method of the herbarium taxonomist has been used forthe interpretation of the species, and an attempt has been made to identify thefruiting specimens with the flowering ones. As far as possible, no intergradingforms have been considered as worthy of specific rank, and I have tried to groupthe "species" into fewer categories of perhaps greater biological reality, in thehope that they will be satisfactory both from a taxonomic and frcm a practicalstandpoint. The key has been so prepared that it should be usable for both thefruiting and the flowering specimens. GENERIC RELATIONSHIPS Heliocarpus L.3 commonly is referred to the tribe Grewieae4 of the familyTiliaceae and usually is recognized by its characteristic fruits. The genus is dis-tinct from the other genera of Grewieae except Triumfetta. There is no difficultyin distinguishing the two genera when both are in fruit, as the fruits are very dis-1An investigation carried out at the Missouri Botanical Garden and submitted as a thesis in partialfulfillment of the requirements for the degree of Master of Arts in the Henry Shaw School ofBotany of Washington University. 2Watson, E. E. The genus Heliocarpus. Bull. Torrey Bot. Club 50:109. 1923. 'Sp. Pl. ed. 1. 448. 1753. 4K. Sch. in Engl. & Prantl, Nat. Pflanzenfam. 1116:29. 1895.(507)
BioStor
