53 
+ + Shrubs or trees, 
3. Choisya. Low unarmed shrubs: leaves opposite (or nearly so), radiately 5 to 
10-foliolate: stamens 8 to 10, 
4, Xanthoxylum. Trees or shrubs, mostly prickly: leaves alternate and pinnate: 
stamens 3 to 5. 
** Ovary entire or slightly lobed. 
5. Ptelea. Shrubs or small trees: leaves opposite and alternate, 3-foliolate: sta- 
mens 4 or 5: fruit orbicular and broadly winged. 
6. Helietta. Shrubs: leaves opposite, 3-foliolate: stamens 3 or 4: fruit of 3 
samaras (winged fruits). 
7 Amyris. Shrubs: leaves mostly alternate, 3-foliolate: stamens 8: fruit a glo- 
bose or ellipsoidal drupe. 
1: PEGANUM L. 
Branching herbs, with alternate many-parted leaves, pale yellow 
flowers on solitary axillary peduncles, conspicuous foliaceous and pin- 
natifid sepals, 12 to 15 stamens, and a globose 3-lobed nearly sessile 
pod. 
1. P. Mexicanum Gray. Stems 20 to 30 em. high, very leafy, pubescent: leaves 
with narrowly linear divisions: peduncle shorter than the flower: calyx and corolla 
4-merous, the 3 to 5-parted leaf-like sepals twice as long as the petals.—Abundant in 
northern Mexico near the Rio Grande, and found in the Eagle Mountains of extreme 
western Texas, 
2. THAMNOSMA Torr. 
Low glandular desert more or less shrubby plants, strongly scented, 
with alternate linear leaves, solitary yellow or purple axillary flowers, 
4 sepals, 4 erect petals, 8 stamens at the base of a cup-shaped lobed disk, 
and a more or less stipitate 2-lobed pod, 
1, T. Texanum Torr. Woody only at base, the slender stems 7.5 to 40 cm. high : 
leaves scattered and soon deciduous: flowers small, on shert naked pedicels, yellow 
tinged with purple: pod very short stipitate, lobed nearly to the middle. (Rutosma 
Texanum Gray.)—From the Colorado to the Rio Grande and west to New Mexico. 
Apparently abundant in the mountains west of the Pecos. 
3. CHOISY A HBK. 
Low unarmed shrubs, with opposite radiately 5 to 10-foliolate leaves, 
white mostly solitary long-pedicelled axillary and terminal flowers, 
small scale-like petals, 8 to 10 stamens, and a 5-lobed 5-beaked pod. 
1. C. dumosa Gray. Low and much branched, pubescent, 9 to 18 dm. high: leaf- 
lets narrowly linear and coriaceous: flowers either solitary or 2 to 4 and umbellate: 
ovary 5-lobed, hairy, the cells produced above into a short incurved beak, with ven- 
trally attached styles; but two of the carpels ripening, these becoming ovate, com- 
pressed and dotted. (Astrophyllum dumosum Torr.)—Mountain cafions in El Paso 
County and adjacent Mexico, 
4. XANTHOXYLUM L. (PRICKLY asu.) 
Shrubs or trees, with pinnate alternate leaves, more or less prickly 
stems and leafstalks, small greenish dicecious flowers, 4 or 5 stamens, 
2 to 5 separate pistils but with conniving styles, and thick fleshy 1 to 
2-seeded pods. 
