Two new species of Cercocarpus are described from limestone areas in the Sierra Madre Oriental in eastern Mexico. Cercocarpus mexicanus appears most similar to the C. montanus complex, but has prominent stomatal crypts as in C. fothergilloides; it differs from both in its thickened leafblades with distinct rows of conspicuous stomatal crypts on the abaxial leaf surface. Cercocarpus rzedowskii is similar to C. ledifolius but differs in the absence of bundle sheath extensions in leaves. In leaf and stem vestiture it has similarities with C. fothergilloides. Recent field studies in Sierra Madre Oriental of Nuevo Leon, Tamaulipas, and San Luis Potosi, Mexico have uncovered two new species of Cercocarpus (Rosaceae) that are chaparral dominants. The species are described herein. Cercocarpus mexicanus Henrickson, sp. nov. (fig. la-c).-TYPE: Mexico, Nuevo Leon, Santa Rita, Galeana, 2100 m, 25 Apr 1981, G. B. Hinton 18191 (holotype: TEX!; isotypes to be distributed).-PARATYPES: Mexico, Nuevo Leon, ca. 15 air km SW of Galeana on W slope of mts. just S of Cerro Potosi above old abandoned settlement at Santa Rita de Cardeladas on limestone slopes with Pinus cembroides, Rhus virens, Lindleya, Mortonia, Garrya, Chrysactinia, Forsellesia, Gochnatia, ca. 2100-2200 m, near 24?46'N lat, 100?13'W long, 10 Oct 1982, Henrickson & Hess 19295 (TEX, MOR, and to be distributed); ca. 30 km ENE of Dr. Arroyo, 2.5 km ENE of San Antonio de Pefia Nevada, W base of Cerro Pefia Nevada, above gypsum on limestone, 6600 ft, 3-5 Aug 1981, Nesom 4294 (TEX). A speciebus omnibus aliis genus laminis foliorum valde incrassatis 0.5-0.8 mm crassis, venis secondariis crassis arcuatis corneis, areis inter venas secondarias cryptis stomatiferis conspicuis 2-4-seriatis instructis differt. Much-branched, erect, obovoid shrubs (0.5)0.7-2 m tall, 0.5-1 m in diam.; stems erect, ascending, many from base; young stems dark maroon, strigose with antrorse hairs 0.2-0.6 mm long, glabrate, with internodes 5-20 mm long; older stems mottled gray-silver; periderm roughened with age; upper stems bearing many ascending to divergent short shoots 1-14 cm long, 1.5-3.2 mm in diam. with internodes ca. 1 mm long, these branching, occasionally reverting to long shoots for 1-2 seasons. Leaves erect-ascending; petioles (1.5)3-5(6) mm long, broadly clasping at very base, 3-angled, canaliculate adaxially above base, strigose as young stems, dark maroon to yellowish-green; stipules maroon-brown, thin but coriaceous, adnate to basal petiole margins for 1-1.5 mm, terminating in acute-acuminate tips 0.5-1(2) mm long, strigose abaxially, glabrous adaxially, eventually deciduous; leaf-blades stiffly coriaceous, elliptical, narrowly ovate, narrowly obovate to ovate, (12)17-31 mm long, (6)10-15(17) mm wide, 0.50.8 mm thick, rounded to obtuse at tips, narrowly to broadly cuneate at bases with lower margins entire, convex, pinnately veined with 4-7 ascending, slightly arcuate secondary veins, each terminating in a serration or dentation (0.5)1-2 mm long in distal one-half to one-third of blade, distal teeth usually reduced, all teeth usually terminating in narrow, blunt, conical, eventually darkened tips 0.2-0.5 mm long; lamina flattened or conduplicate, folded along lower midrib, weakly strigose, subglabrate, green to yellow-green on both surfaces; midveins and often secondary veins impressed above, yellowish, corneous, flattened, 0.4-0.6(1.0) mm wide, sparsely sericeous beneath; secondary veins 0.41.2(1.7) mm apart, separated by distinct bands of stomatal crypts in (1)2-4 irregular rows beneath (fig. 2b-c), crypt openings circular or variously elongate, 0. 1-0.4(0.7) mm long, with marginal rims flattened in fresh or hydrated leaves, slightly raised in dried leaves, densely sericeous on inner rims with white, straight hairs that extend into crypts (fig. 2a). Flowers 1(3) in axils of leaves or reduced bracts; bracteoles textured and colored as stipules, conduplicate