1953] 



REVISION OF MACROLOBIUM 



261 



Petiolules. Petiolules are infrequent and when present constitute a very usa- 

 ble characteristic; a few isolated examples occur in each of the sections. The 

 terra is herein applied to that portion, when present, of the leaflet below the last 

 sensible trace of the blade. 



Rachis Rudiment. In a few of the uni jugate species, M. pendulum for example, 

 the last vestige of the rachis persists as a subulate structure as much as a centi- 

 meter or more in length. It is generally caducous, but in the species named it is 

 persistent or semi-persistent. 



Leaflets. In form and dimensions there is the greatest diversity in these 

 parts. In the more primitive species the form is mostly oblong and it is in the 

 more highly evolved forms that other shapes occur. Both size and shape of the 

 leaflets have been used systematically, but of greater importance is the number 

 of pairs per leaf. They are always opposite and always in pairs except in some 

 forms of M. campestre in which one of the leaflets of the terminal pair does not 

 develop; the latter condition is referred to as pseudo-imparipinnate. The evolu- 

 tionary tendency is toward a progressive reduction in the number of pairs with 

 usually a corresponding increase in the leaflet size. However, this tendency has 

 been expressed repeatedly and independently of all other characters. 



The details of the venation are so uniform that they seldom furnish useful 

 characters. However, characters of secondary importance are found in the degree 

 of prominence of the costa (the "midrib' * of the leaflet); in M. limbatum the pri- 

 mary vein branches (the first-degree branching of the costa) anastomose intramar- 

 ginally to form a distinct submarginal vein, and such intramarginal nerves are also 

 found in M, retusum. In M. furcatum and M. flexuosum the venules (the venation 

 other than the costa and primary veins) are prominent, numerous, and closely 

 parallel. 



The' vesture of the leaflets is quite variable and is used infrequently in the 

 following treatment. The leaflets may be entirely glabrous or pubescent only on 

 the costa or throughout. The under surface is commonly, but not always, covered 

 by a persistent microscopic waxy bloom. 



In a few taxa glandular punctae are present and are sufficiently constant to 

 justify their use as a taxonomic character. These glands occur as small puncta- 

 tions of regular form and of uniform distribution over the lower leaflet surface. 



Inflorescence. The inflorescence may be axial or terminal and ramiflorous or 

 cauliflorous; the latter pair of characters is particularly useful taxonomically on 

 the specific level. It is always racemose but considerably variable in dimensions 

 and outline. In M. furcatum one or two short lateral racemes occur regularly to- 

 ward the base of the inflorescence, but these are rare in other taxa. 



The peduncle of the inflorescence is generally very short or absent but in M. 

 multijugum and M. molle one as long as five centimeters is produced, which serves 

 to distinguish these species. 



Bracts occur regularly at the base of each pedicel, but these vary from minute, 

 insignificant structures to those which surpass the flowers in length. They fre- 

 quently furnish characters of some systematic importance in their size, form, and 

 vesture. They are most frequently very early caducous but are persistent in sev- 

 eral taxa; in parvifolium, for example, they persist as a wide band of imbricate 

 sterile bracts at the base of the inflorescence. 



The flowers are always borne on pedicels, at the apex of which are found two 

 bracteoles which are connivent marginally to enclose the flower before anthesis. 

 These bracteoles are variable in form not only between but also within taxa, but 

 for taxonomic purposes they are much more reliable in their dimensions. At an- 

 thesis they open to the base along an adaxial and an abaxial line, releasing the 



