428 swingle: new genus pleiospermium 



small spiny trees. Paramignya and Lavanga have similar fruits, 

 but are woody lianes with recurved spines and aberrant leaf charac- 

 ters. The genus Pleiospermium differs from Pamburus in having 

 thinner, netted-veined, usually trifoliolate leaves, with the lamina 

 articulated with the petiole, instead of thick, nearly veinless, unifolio- 

 late leaves and the lamina not articulated with the petiole ; furthermore, 

 Pleiospermium has the ovary seated on a small annular disk, while 

 in Pamburus the disk is prominent and cylindric. The flower, fruit, 

 and seed characters of Pleiospermium are very different from those 

 of Merope. Pleiospermium is only rather remotely related to Hes- 

 perethusa, Triphasia, and Severinia, which all have very small red or 

 black berry-like fruits and the leaves also very different. 



Pleiospermium (or at least P. dubium) differs, so far as known, 

 from all its relatives among the small, soft-rinded, gummy-celled group 

 of citrous fruits in having short and slender pulp vesicles arising 

 from the inner wall of the ovary. In this respect it resembles the sub- 

 genus Rissoa 5 of the genus Atalantia, belonging to a different subtribe, 

 but it differs from that and from the other true citrous fruits in having 

 the cells of the fruits filled with an aromatic, sticky fluid. A thorough 

 study of the anatomy and morphology of the fruits of all of these 

 genera is urgently needed in order to classify them in natural groups. 



Pleiospermium seems to be a primitive genus, showing analogies with 

 many rather diverse groups. It even shows a certain analogy in its 

 leaf characters with the Philippine Chaetospermum, 6 one of the hard- 

 shelled citrous fruits belonging to another distinct subtribe. 



Two closely related species of Pleiospermium are known, one from 

 southern India and Ceylon, the other from Java. 



KEY TO THE SPECIES 



Leaflets usually 3, obtuse; ovary glabrous 1. P. alatwm. 



Leaflets 1, 2, or 3, acute or acuminate; ovary pubescent. . 2. P. dubium 



1. Pleiospermium alatum (Wight & Arn.) Swingle 



Limonia alata Herb. Madr. Wall. Cat. no. 6363. 1832 (nom. nud.). 

 Limonia alata Herb. Madr. Wight Cat. no. 324. 1834 (nom. nud.). 

 Limonia alata Wight & Arn. Prodr., 1: 92. 1834. 

 Illustrations: Wight, 111. Ind. Bot., 1: pi. 41 (1840); Beddome, FL 

 Sylvat., Outlines Bot., pi. 8, fig. 3. 



Type locality: "Foot of the Neelgherries," Madras Presidency, 

 southern India. 



5 Swingle, Walter T. Atalantia, in Bailey, Standard Cycl. Hort., 1:426. 

 1914. 



6 Swingle, Walter T. Chaetospermum, a new genus of hard-shelled citrous 

 fruits. Journ. Wash. Acad. Sci., 3: 99-102. 1913. 



