1953] 



REVISION OF MACROLOBIUM 



259 



3. Foliar axis usually narrowly alate. 



4. Claw of petal usually auriculate. 



5. Fruit always smooth. 



3. Foliar axis non-alate. 



4. Claw not auriculate. 



5. Fruit smooth or with transverse lines. 



In a second letter, Dr. Leonard suggested that the number of petals, presence 

 or absence of staminodia are the important characters which with the geographic 

 distribution serve to separate these groups of species. He referred again, how- 

 ever, to the American species as possessing one large petal, sometimes accom- 

 panied by one to four small petals. The present writer considers the latter not as 

 "small petals" but petalodia, that is, vestigial remnants of petals. 



The point, morphologically, at which a petal becomes a petalodium is indeed 

 obscure, but anatomical evidence has led the writer to the conviction that these 

 bodies are more properly referred to as vestigial structures. Several of the Ameri- 

 can species were studied by means of transverse serial sections, and while the 

 one large adaxial petal had a very obvious vascular supply in all the flowers of 

 the few species studied, no sign of bundles for either vestigial petals or stami- 

 nodia was observed. Whether or not the more prominent petals of the African spe- 

 cies have a vascular system is not known, but in the American ones it appears 

 that there is not more than one vascularized petal and furthermore the vestigial 

 non-vascularized ones are deciduous at anthesis if formed at all and in any case 

 are seldom observed. 



Recently it was decided to attempt to secure additional data which might as- 

 sist in the resolution of this problem of generic delimitation. Accordingly, Dr. G. 

 Erdtman of the Palynological Laboratory at Bromma, Sweden, was asked to make 

 available any information which he might have on this genus. He very kindly of- 

 fered to undertake a study of the pollen morphology of the genus; for this immeas- 

 urable assistance I express my sincerest appreciation. 



Material of thirteen African and nine American species was sent to Dr. Erdt- 

 man for his study. A preliminary report was received within a few weeks, with the 

 statement that "the grains can be classified in two groups: South American spe- 

 cies and African species." He pointed out that in both species-groups the sexine 

 is conspicuously striate but that the striae in the American species are much 

 more densely spaced than those of the African species. Further differences were 

 found in the form of the striae and in the relative length of the baculae. These 

 characters are apparently constant for each species-group, and, while micro- 

 scopic, they lend valuable support to the arguments for maintaining the African 

 and American species in separate genera. 



In summary, Dr. Leonard contends that the occasional presence of "petals" 

 and staminodia in the American species form a bond with the African species with 

 their five petals and omnipresent small stamens and/or staminodia, for which 

 reason they should be considered congeneric. The present writer maintains that 

 the characters enumerated in the table above and the palynological characters are 

 sufficient for the generic separation of these two groups. Macrolobium is here 

 considered to be an American genus with its closest relatives the species in Af- 

 rica formerly assigned to it; whether these latter species be referred to one genus 

 or more than one is a problem for the students of the African floras to resolve. 



HISTORY OF THE GENUS 



Aublet in his publication on the plants of French Guiana (1775) described two 

 new genera, Vouapa and Outea, the former with two species and the latter with 

 one. Vouapa bi folia is recognizable from the description and plate, but the second 

 species, V. Simira, is probably not congeneric. Although the type of Outea guia- 



