Plant cespitose, forming dense cushions to 3 dm wide and 1 dm high, the interstices packed solid with soil. Stems 2-5 mm thick, each branch with a rosette of ca. 5- 15 leaves and covered below with persistent dead leaves. Leaves oblanceolate to linear-oblanceolate or occasionally spatulate, mostly acute, entire or commonly 1-3-dentate on each margin above, 0.5-3.5 cm long, 1 -5 mm wide above, 0.5-1.5 mm wide above the broadened base, subglabrous or (in the same plant) commonly glandular-puberulent with pluricellular trichome ca. 0.1 mm long, the teeth spreading or lightly reflexed, triangular, the upper mostly longer, to 1 mm long, the midrib prominent, the lateral veins obscure. Peduncle terminal 0.5-5 (-8) cm tall, slender, striate or angled, glandular-puberulent, often with 1 or 2 small lanceolate bracts above. Heads solitary, 10- 12 mm high, 14-21 mm wide, with 5-8 but commonly 6 florets, flowering May to July. Involucre cylindric, 7-9 mm long, 2-3 mm wide, of 5-9 but mostly 6 equal bracts and 3-5 graduated shorter ones, the bracts lanceolate, acute to narrowly rounded , 1-2 mm wide, green or purplish wi th scarious margin , minutely granular-glandu lar and often also sparingly glandular puberulent, the longer ones sparsely villous at apex. Receptacle shallowly pitted, glabrous. Corolla 7-13 mm long, the tube whitish, 2.5 -4 mm long, with a few scattered trichomes ventrally above, the ligule light to deep pink or rarely white, elliptic oblong, truncate and 5-lobed, 4.5 -9 mm long, 2 .5 -4.5 mm wide, the lobes 1-1.5 mm long and a third as wide, triangular-ovate, obtusish. Anthers 3.5-5 mm long, sagittate at base; pollen white. Style 7- 12 mm long, lavender above, ascending puberulent, the style branches ca. 1 mm long. Achenes light tan, pentagono-prismatic, only slightly na rrowed towards base and apex, 2.5 -3 mm long, 0.8-1.0 mm thick , the sides slightly channeled or nearly flat except for a straight shallow longitudinal groove ca. 0.1 mm wide, the angles sparsely and minutely ascending scaberulous Pappus persistent. white, 4-6 mm long, double, the inner bristles ca. 20, stiff, slightly widened and connate at base. plumose nearly to base with pinnae 0.3-0.5 mm long, the outer bristles inconpicous, alternating, very slender, smooth or scaberulous, mostly less than 1 mm long.
Type collection . - Common in crevices of north- and east-facing rocks and cliffs at 2800 meters elevation , Cerro "2828", east rim of the Sierra San Pedro Martir, Baja California, Mex ico (near 31 °02'N, II 5°2 7'W), 5 J uly 1968, Moran 15261 holotype: SD 68877; isotypes: K, MEXU, UC, US, etc.
Distribution. - Known only from the type locality. Other collections: 15064, 15332, 15403. 16533.
Discussion. - This plant appears to be quite limited as to habitat: despite wide collecting in the general area on several trips, I fou nd it only in the one place. However, there a re severa l similar cliffs on the east rim where it probably can be expected. Associated species include Selaginella aspre//a Maxon, Sedum niveum Davids., Heuchera leptomeria var. peninsularis Rosend., Butt., & Lak. , Saxifraga eriophora S. Wats. , Potenti/la whee/eri S. Wats. , Haplopappus pulvinatus Moran, and Tanacetum bajacalifornicum Moran.
Stephanomeria monocephala differs from others of the genus in its polster habit and solitary heads. The regu lar outer series of minute pappus bristles a lso is noteworthy; but although the pappus of Stephanomeria is a lways described as uniseriate, a variable number of similar tiny bristles occurs in several other species.
In other floral and fruiting characters, S. monocephala appears to be an average member of the genus. However, it differs from ever y other species in some combina tion of characters of involucre, flowers, achenes, and pappus. Mr. Leslie D. Gottlieb, a student of the genus, suggests that it is closest to S. lactucina A. Gray, native from eastern Oregon to Nevada and the Sierra Nevada. That is a larger plant, with stems arising singly from slender rootstocks and usually bearing several heads; the heads are larger, with more and larger florets; and the achenes are larger.