(Plate CXXXIX)

Slender, diffuse or prostrate herbs, perennial but precociously flowering, from a slender but eventually woody root, the ±3-9 stems mostly 1-15, rarely to 20 cm long, 1-2-cephalous, the longer ones radiating from the root-crown, simple or few-branched, the shorter ones (and the subradical spurs, if present) erect-ascending, strigulose- pilosulous throughout with stiff straight appressed and narrowly (or a few longer widely) spreading hairs up to 0.6-1 mm long, the inflorescence pilose-barbate, the leaves greenish-cinereous or canescent, the leaflets either pubescent or glabrate above; leaf-spurs 0.5-1 mm long; stipules linear-lanceolate, erect or outwardly curved, 2-6 mm long, pilosulous, becoming stiff and brownish; leaves petioled, 1-3 (3.5) cm long, the narrowly margined, sometimes obscurely punctate petiole and rachis together 0.5-2.5 cm long, the 3 leaflets linear-oblanceolate or -elliptic, acute or subacute, 4-16 (20) mm long, the stalked terminal one longest, all usually ± folded; spikes sessile or shortly pedunculate, the peduncles not over 1 cm long, all terminal or the earliest becoming leaf-opposed, moderately dense, ovoid or oblong-ovoid, without petals 9-14 mm diam, the pilosulous axis 0.5-2.5 (3.5) cm long; bracts deciduous only with the ripe pod, 5-6 mm long, loosely silvery-pilose, the tube 2-2.3 mm long, slightly recessed behind banner, the ribs (like the teeth) reddish or livid, slender, the pallidly membranous intervals charged with 1 row of ± 4 small transparent glands, the deltate- aristate, plumose teeth 3-3.7 mm long, stellately spreading in age; petals clear yellow, fading reddish- or orange-brown, eglandular, the epistemonous ones perched a little below middle of androecium; banner 2.8-3.8 mm long, the linear claw 1.9-2.4 mm, the reniform emarginate or obcordate and subacute blade 1.2-1.6 mm long, 1.4-1.9 mm wide; wings 1.8-2.5 mm long, the claw 0.6-1 mm, the obliquely ovate, bluntly short-auriculate blade 1.2-1.6 mm long, 1.4-1.9 mm wide; keel 3.1-3.9 mm long, the claws 1.1-1.4 mm, the obliquely obovate or oblong-obovate blade 2.1-2.8 mm long, 1.4-1.9 mm wide; androecium 10-merous, 4.5-6 mm long, the longer filaments free for 1-1.4 mm, the pinkish-brown anthers (0.3) 0.35-0.5 mm long; pod (of the section) 2.5-2.8 mm long; seed olivaceous or castaneous, smooth and glossy, 1.7-2.1 mm long; 2n = 14 (Mosquin).— Collections: 17 (vii).

Low hills and plains, in grama grassland and thorn-cactus forest on limestone, 1200 -2230, perhaps 2730 m (3600-6700 or 8200 ft), widely dispersed but relatively uncommon (or overlooked), along the arid w. slope of Sierra Madre Oriental and adjoining Meseta Central from s.-e. Coahuila (mpo Ramos Arizpe) and adjoining Nuevo Leon (mpo Galeana) to n. Queretaro (mpo Cadereyta), w. into n.-e. Durango (mpos Rodeo and Cuencame) and n.-e. Zacatecas (mpo Mazapil), in Sierra Madre just entering Tamaulipas (Miquihuana, here reported from 8200 ft); disjunct in the Tehuacan desert in s.-e. Puebla. — Flowering June to November. —Representative: Durango: Mosquin et al 6902 (NY); Ripley & Barneby 13,504 (MEXU, NY), 13,510 (CAS, NY). Coahuila: Ripley & Barneby 13,521 (NY). Nuevo Leon: Bierner & Turner 96 (NY). Zacatecas: Ripley & Barneby, s. n. (NY). San Luis Potosi: Purpus 5191 (F, NY, UC); Ripley & Barneby 13,318 (CAS, MICH, NY, US), 14,768 (CAS, MEXU, NY). Tamaulipas: Stanford, Retherford & Northcraft 789 (ARIZ, MEXU, NY, UC). Queretaro: Rose, Painter & Rose 9788 (MEXU, NY, US). Puebla: Ripley & Barneby 14,715 (CAS, DAO, NY).

Dalea luisana (of San Luis Potosi) Wats., Proc. Amer. Acad. 17: 341. 1882 ("Luisana").—"In the San Miguelito Mountains (808, Schaffner); it is also 164 Parry & Palmer, referred to D. wrightii" — Holotypus, GH! isotypi, renumbered 603/808, M, NY! — Parosela luisana (Wats.) Vail, Bull. Torrey Club 24: 16. 1897; Rose, Contrib. U. S. Nat. Herb. 10: 105. 1906.

Dalea ternata (three-parted, of the trefoil leaflets) T. Bdg., Univ. Calif. Pub. Bot. 3: 380. 1909. — "Collected near Barranca de Tlacuilosto [near San Luis Tultitlanapa, mpo Caltepec, Puebla, near the Oaxaca boundary]. No 3214." — Holotypus, collected by C. A. Purpus in june 1908, UC! isotypi, F, NY!

The species of sect. Cylipogon described up to this point are characterized by pinnately 5-foliolate leaves; with D. luisana begins the series of species with leaves all or nearly all either pedately or palmately trifoliolate. In the latter series D. luisana seems most nearly related to the endemic Texan D. hallii, like it in the wiry, appressed-pilosulous stems and linear to linear-elliptic leaflets, but different in substantially larger flowers. The species varies little. The populations in the Tehuacan desert, although far separated from the main range of their species, are essentially typical, as already inferred by Rydberg (1920, p. 97).