APR. 1960 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 10(2):38-57 



THE MORPHOLOGY AND RELATIONSHIPS OF DIOMMA, 



GEN. INC. SED. 



William L. Stern and George K. Brizicky 



Samuel James Record Memorial Collection 

 School of Forestry, Yale University 

 New Haven, Connecticut 



INTRODUCTION 



In natural systems of plant classification, an attempt is made to arrange 

 plants so that related taxa are near to one another. The bases upon which deci- 

 sions are made concerning relationships among plants are various, and features 

 that are important in some groups are relatively unimportant in other groups. 

 It is now regarded of utmost importance in phylogenetic considerations to select 

 not a single character upon which to found relationships among taxa, but to 

 obtain information from as many pertinent fields of endeavor as possible, and 

 to bring these data to bear upon problems in classification. This synthesizing 

 of available information has been accomplished with more or less success for a 

 number of taxa. Nevertheless, there are still many enigmatic, incompletely 

 investigated groups which have remained in a state of taxonomic limbo affiliated 

 at one time with one category and at other times with other categories. Such has 

 been the case with Diomma, genus incertae sedis, noted by Engler from speci- 

 mens collected by Ule in 1910, but actually published by Harms (1931a). 



It was suggested recently by Dr. Bassett Magnire of The New York Botanical 

 Garden, that a combined morphologic-taxonomic study of Diomma be made in an 

 effort to determine its relationships. In the course of correspondence regarding 

 specimens of Diomma, Dr. Richard S. Cowan of The United States National 

 Herbarium recommended that we also investigate the genus Sohnreyia in this 

 regard. Dr. Cowan remarked, that at least superficially Diomma and Sohnreyia 

 appeared remarkably alike. At the present time descriptions of two species of 

 Diomma appear in the literature, and it will remain to be shown whether these 

 represent distinct taxa and also whether other species perhaps exist. 



Diomma* 



Diomma ulei Engler ex Harms remained the only species until 1952, when 

 Steyermark described a second species, D. fruticosa. Diomma comprises trees of 

 striking appearance for dicotyledons. The unbranched trunk is surmounted by a 

 crown of large pinnately compound leaves and the trees greatly resemble palms 

 in habit. According to Maguire's field observations, at maturity the plants are 

 crowned by a large compound paniculate inflorescence. Apparently the plants 

 die after the fruits mature. 



Harms (1931a) describes Diomma ulei as possessing large pinnately com- 

 pound leaves. Flowers are white, regular, bisexual, 5-merous, arid borne in short 

 panicles (sic). The free stamens oppose the sepals, and are broadened at the 

 base of the filament. The broad ovary is laterally compressed, 2- or rarely 3- 

 locular, and borne on a broad, cushion-like, nectariferous base. Locules are 

 uniovulate. Ovules are anatropous, and hang from the upper portion of the 

 septum on a short, thick funiculus so that the raphe is dorsal and the micropyle 

 inside (fig. 1A). This condition has been termed apotropy. Styles are 2, very 

 short and stout, each terminated by a capitate stigmatic surface. Samaras are 



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