1953] 



REVISION OF BRACHYOTUM 



349 



most obviously roughened, and those of the upper leaf surface and primary veins 

 of the lower leaf surface the least. The individual hair has the greatest develop- 

 ment of roughening basally, the least apically. The bases of the hairs are more or 

 less "adherent" to the leaf surface, actually being subepidermal, and are some- 

 times radicine; the adherence is best developed in the trichomes of the upper leaf 

 surface. Calcium oxalate deposits can be seen in the hair bases as round white 

 dots; these deposits have also been occasionally observed, apparently subepi- 

 dermal^, on the hypanthium. The trichomes are sometimes on low to well-devel- 

 oped callosities (best developed on the upper leaf surface) which are usually dis- 

 tinguishable from the hair bases. Well-developed callosities (tubercles) are often 

 in regular lines on the upper leaf surface; the number of these longitudinal rows 

 at the widest part of the leaf blade has been utilized as a diagnostic feature. The 

 hairs sometimes have swollen (glandular) tips, the frequency of occurrence of 

 such hairs varying with location on the plant; the petal cilia are the most fre- 

 quently gland-tipped, followed by the hypanthial, lower leaf surface, and stem 

 hairs; the maximum development occurs in B. lutescens where even the upper leaf 

 surface hairs are sometimes glandular. Small, few-ce lle4 brownish, short- to 

 elongate-clavate glands, mostly 0.05-0.15 mm. long, are always present on the 

 lower leaf surface. These glands occur singly or in clusters of up to ten; the clus- 

 ters are often at the bases of hairs and with age often turn black, forming irregu- 

 lar "punctae." The glands also generally occur sparsely on the hypanthium and 

 calyx, being especially noticeable in the axils of the sepal cilia, and only rarely 

 and sparsely on the upper leaf surface. Pflaum (1897) studied in detail the anat- 

 omy of the leaves and pubescence of the Tibouchineae and Microliciae; his dis- 

 cussion and drawings of various genera well mirror the range of variation in mela- 

 stome hairs. Trichomes of various species of Brachyotum are illustrated in Fig- 

 ures 1—22 of the present revision. 



The hairs are most frequently appressed, sometimes patent; the degree of ap- 

 pression or patency is probably environmentally determined and is not a reliable 

 diagnostic feature. The term "strigose" has been limited to pubescence of ap- 

 pressed trichomes averaging more than 1 mm. long; "short-strigose," 1-1.5 mm.; 

 "strigulose," less than 1 mm.; "long-strigulose," 0.5-1 mm.; and "short-strigu- 

 lose," less than 0.5 mm. Patent (spreading) pubescence has been described as 

 "hirsute," "hirsutulous," "setose" (with stout stiff hairs), or "setulose," the 

 st7:es of these hairs being indicated in the individual descriptions. 



Habit and Branching. All species are low shrubs or shrubby trees 0.5-8 m. tall, 

 with the branching loose to fastigiate. The young branchlets are obscurely to 

 markedly quadrangular, becoming rounded with age. The branchlets decorticate in 

 about the third growth season, an inner tan to red-brown cork then being exposed. 



Leaves. Petioles are canaliculate, with pubescence the same as that of the 

 branchlets but generally shorter or lacking on the upper surface. The only dimen- 

 sion cited for petioles in the specific descriptions is the length. 



Blades vary in texture from chartaceous (B. gracilescens , B. rugosum, part of 

 B. microdon) to thick-coriaceous or thick-brittle; the margins are usually conspic- 

 uously recurved, except in the thin-leaved species. The longitudinal conspicuous 

 veins (primaries) range in odd number from three to seven; sometimes there is an 

 additional pair of indistinctly developed submarginal veins (marginals), formed by 

 coalescence of the ascending ends of the secondaries. Secondaries are usually 

 inconspicuous and rather irregular, sometimes conspicuously reticulate. The pri- 

 maries are impressed above and elevated below, the secondaries inconspicuously 

 so. The area along the veins on the upper leaf surface is less pubescent than the 



