376 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
The individual species differ from those of Abronia in that they often extend 
over relatively large areas; wide distribution seems to be characteristic of a 
majority of the species. B. erecta is a good example of such distribution. 
Doctor Heimer] divided the genus (as it is defined here) into two sections, 
the first, Pterocarpon, containing B. pterocarpa (several other related species 
such as B, alata and B. megaptera should be included here); and the second, 
Micranthae, including the rest of the species. The two sections are hardly 
worthy of being maintained. The wings of the former section differ from the 
ridges of the second merely in degree and it would be difficult to tell to which 
some of the species should be referred. The genus as it is defined here is com- 
posed of closely related species and is the most satisfactory of the large genera 
of the family in this respect. ' 
KEY TO THE SPECIES, 
Fruit with distinet, rather thick, not membranous 
wings; annuals; flowers umbellate. 
Umbels either axillary or terminal, but never pani- 
B, pterocarpa, 
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Umbels arranged in panicles. 
Wings of the fruit only slightly narrowed be- 
low; umbels with only 2 or 4 flowers or the 
flowers frequently solitary; flowers 8 min. 
long_-----------__-_--________ ee 2. B. alata. 
Wings of the fruit considerably narrowed be- 
low; umbels containing 5 or 6 flowers; 
flowers about 1 mm. long____--_----------_. 3. B. megaptera. 
Fruit not winged; the ribs sometimes almost wing-like, 
but very thick and coriaceous. 
Flowers 5 mm, wide or more; perennials. 
Leaves ovate or oval___-__-__-~_-_________ —.. 21. RB. anisophylla. 
Leaves linear or narrowly lanceolate. 
Margins of the leaves strongly revolute; 
leaves thick; stamens mostly 5 -___~_-__ 22. LB, tenuifolia, 
Margins of the leaves not revolute or 
but slightly so; leaves broader and thin; 
stamens mostly 3; plants larger and 
stouter. 
Stems hispid below, glandular above_ 23. B. linearifolia. 
Stems glandular-pubescent throughout. 23a. 2. linearifolia 
glandulosa. 
Flowers less than 5 mm. wide. 
Flowers solitary at the ends of the peduncles; 
perennials. 
Fruit glabrous; flowers about 1 mm. wide. 19. B. organensis, 
Fruit viscid; flowers from 38 to almost 5 
mm. wide____-_-_-___________________-. 20. B. gracillima, 
Flowers not solitary at the ends of the 
branches. 
Flowers umbellate or subumbellate at the 
ends of the peduncles. 
Fruit glabrous; annuals. 
Fruit subtended by conspicuous, per- 
sistent, large bracts; plants gland- 
ular_--__-__---~---------------- 9. B. purpurascens, 
