32 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN calyx 5-9 mm long, extemaUy glabrous to variably pubescent, the hypanthium 1.5-3 mm deep, the tube (measured to a lateral sinus) 3-4.5 mm long, the ribs becoming bluntly prominent, the firm intervals charged with smaU brownish glands, the 2 broad ventral intervals with ± 2 rows, the rest with 1 row of ± 3-5 glands, the teeth dissimi­ lar, the ventral pair broadly lanceolate to triangular short-acuminate, 2-4.5 mm long (1 mm shorter to 0.5 mm longer than tube), (1.2) 1.4-2 mm wide near base, the rest lanceolate, ± half as wide, the dorsal one often shortest, the sinus behind the banner commonly much shaUower than the rest; petals indigo-blue or violet-purple, glandless, deciduous; banner 6.3-10.S mm long, its claw very short, its blade flabeUate or flabel­ late-obovate, deeply retuse, at base either cuneately tapering or subauriculate; wings a trifle longer than banner, the claw 2.2-3.6 mm long, the broadly oblong or oblong- obovate, obtuse or subemarginate blade 5.4-8.2 mm long, 2.2-3.5 mm wide; keel usu­ ally a trifle longer than wings, rarely a little shorter, 8.2-11.2 mm long, the claws 2.6- 3.7 mm, the obliquely obovate blades 5.9-8.2 mm long, 3.3-4.9 mm wide; androecium (5.5) 6.5-9.8 mm long, the filaments free through (3) 3.5-5.6 mm, the anthers (0.85) 0.9-1.3 mm long; pod obliquely ellipsoid or ovoid-eUipsoid, the subcompressed body 8-10 mm long, (3.6) 4-6 mm diam, at least beyond the middle 2-carinate by the su­ tures, the convex valves charged with large, round or broadly elliptic blister-glands, between the glands either viUosulous or glabrous, the ventral suture cUiolate; seed (4.7) 5-6 mm long.

These are small , never arborescent as suggested by the inappropriate epithet, and diverse in aspect because so variable in pubescence, in configuration of the leaves, and in flower- size. The species differs as a whole from the closely related Ps. schottii in its smaller stature and usuaUy pinnate (not simple or trifoliolate) leaves, always excepting the anomalous Ps. arborescens var. simplifolius, discussed in more detail below and in relation to Ps. schottii itself. Over a great part of the Mohave Desert in and west-central Ps. arborescens is the only member of sect. Xylodalea and with the exception of Ps. polydenius the only Psoro­ thamnus, and like the latter is found chiefly, perhaps exclusively, on granitic and volcanic bedrock. On the calcareous ranges of far southeastern Mohave it is replaced by the vicariant and perhaps too closely related Ps. fremontii, distinguishable by no feature of moment up to the distinctive pod. The pods of all forms of Ps. arborescens are Uke those of Ps. schottii charged with relatively few, large, circular blister-glands scattered over an eglandular field in polka-dot patterns. In D. fremontii the pod valves are covered by small orange glands of indeterminate size and shape which run together into irregular lines or ridges, the surface appearance being that of caramelized sugar. Beyond the limits of the Mohavean floristic province Ps. arborescens is represented by two distantly isolated populations, one relatively extensive in the valley of Colorado River upstream from Grand Canyon in northern Arizona, the other dramatically disjunct on the Sonoran shore of Gulf of California, where it has been collected in only one station. The latter, surprisingly, cannot be distinguished at present from typical Ps. arborescens of southwestern Mohave Desert. The Arizona appears below as Ps. arborescens var. pubescens.

Key to the Varieties of arborescens

1. Calyx 7-9 mm long, the tube 3.6-4.5 mm, the ventral pair of teeth 3-5.4 mm long; relatively local in three disjunct areas: s.-w. Mohave Desert in w. San Bernardino and adjoining Kern counties, California; n.-w. Sonora; n.-centr. Arizona. psorothamnus sect, xylodalea 33

2. Leaflets (3) 5-7, mostly rhombic-ovate to broadly lanceolate, often partly con­ fluent with the rachis, the widest on the individual plant well over 2.5 mm wide: foliage either vUlous-tomentulose or glabrate; Mohave Desert and Sonora. 4a. var. arborescens. 2. Leaflets (5) 7-11, linear or narrowly oblanceolate, none over 1.5 mm wide; foliage silky-strigulose; n.-centr. Arizona. 4d. var. pubescens. 1. Calyx 5-6.8 mm long, the tube 3-4.2 mm, the teeth 1.8-3.7 mm long; n. Colorado to n. Mohave Desert, Owens and Death vaUeys, and Mineral County, Nevada, local in Coachella and San Jacinto valleys and vicinity. Riverside and s. San Bernardino counties, California. 3. Calyx-tube glabrate or only minutely puberulent; leaflets loosely pubescent to glabrous, of an ovate or lanceolate type, mostly acute, some at least 2.5 mm wide; n. Kern, Inyo, Mono counties, CaUfornia, and adjacent Nevada. 4b. var. minutifolius. 3. Calyx-tube silky-canescent; leaflets of linear-oblanceolate type, mostly less than 2 mm wide, aU usually silky-strigulose and decurrent into the rachis; Co- chella and San Jacinto vaUeys about s. foothUls of San Bernardino Mountains and vicinity. 4c. var. simplifolius.

4a. Psorothamnus arborescens (Torrey) Barneby var. arborescens (Plate IV)

Variable in pubescence, the foliage either densely vUlous-tomentulose or only thinly pilosulous, gray or green; young branchlets usually purplish, the old becoming brown and furrowed; leaves 1-3.5 cm long, the (3) 4-7 leaflets ovate to obovate or elliptic, often asymmetrically so, obtuse, emarginate, or bluntly gland-mucronulate, (3) 5-10 mm long, the 3 uppermost of all leaves usually decurrent and often irregularly conflu­ ent, but sometimes all free and the lateral ones all jointed; flower large, the calyx as given in key; petals indigo blue, the banner 9-10 mm, the keel 10.2-11.4 mm, its blades 8.2-8.4 mm long; pod either glabrous except for a few hairs along the ventral keel or thinly villosulous; androecium mostly 8.8-9.8 mm long, the filaments free for 4-5.6 mm.— Collections: 22 (i). Desert hiUsides and stony flats in the Larrea belt, on granitic bedrock, sometimes with Yucca arborescens, 390-780 m (1300-2600 ft), locally plentiful in scattered sta­ tions on s.-w. Mohave Desert in w. San Bernardino and adjoining Kern counties, Cali­ fornia (approximately within the triangle formed by towns of VictorvUle, Barstow, and Randsburg); greatly isolated near sea-level on shore of Gulf of California in n.-w. So­ nora (Puerto Pefiasco, lat. ± 30° 40'N). —Flowering April and May.—Representa­ tive: UNITED STATES. California. San Bernardino: Wolf 3418, 3419 (SD); Hall 6160 (NY, UC), 6197 {\JC); L. S. Rose 12,055, 12,058 (CAS, NY); Hall & Chandler 6851 (UC); Ripley & Barneby 5206 (NY). MEXICO. Sonora:L. H Cook in 1934 (SD).

Psorothamnus arborescens (Torr.) Barneby, comb, nov., based on Dalea arborescens (becoming treelike, a misnomer, taken from Fremont's label) Torr. ex Gray, Mem. Amer. Acad. II, 5: 316. 1854. — "Mountains of San Fernando, a southern branch of the Sierra Nevada, California; AprU, Fremo«^." —Holotypus, dated AprU 14, 1844, NY (herb. Torr.)! isotypus, GW\—Parosela arborescens (Torr.) A. HeU., Cat. N. Amer. PI. ed 2, 5. 1900. Psorodendron arborescens (Torr.) Rydb., N. Amer. Fl. 24: 42. 1919.