One of the most beautiful, also one of the smallest, cacti of the Chihuahuan Desert is Epithelantha. Usually it grows in open desert, often half hidden in the limestone slabs. Several species and varieties have been proposed because the cacti are extremely variable, especially with respect to spination and whether stems are solitary or caespitose. Superficially, Epithelantha looks like Mammillaria, but Norman Boke (1955) found that the structure of the areole is very different. Whereas the areoles of Mammillaria are clearly dimorphic, with flowers arising at the bases of tubercles, those of Epithelantha are not, for flowers arise from the spine-producing portion of the areoles at the tips of the tubercles. However, Boke also discovered that other developmental processes in Epithelantha are similar to Mammillaria. He suggested that Epithelantha is closely related to Mammillaria, or that there has been parallel evolution.

Epithelantha was discovered on the boundary survey led by William H. Emory and described by George Engelmann in 1856 as Mammillaria micromeris. Engelmann also described variety greggii, believing it to be "larger and coarser" than the typical variety. In 1898 Frédéric Weber listed "Epithelantha" as a synonym of M. micromeris, not formally proposing it as a distinct genus. Nathaniel Britton and Joseph Rose described it as a genus in 1922 (type, M. micromeris = E. micromeris), accepting a single species. The name Epithelantha is derived from the Greek epi, upon, thele, nipple, and anthos, flower, thus flower upon the nipple or tubercle.

Most taxonomists now believe that there are but two species, one with five subspecies. Charles Glass and Robert Foster (1978) published a revision of the genus, commenting that the limited range and distribution of the genus and the relatively minor differences between the proposed taxa within the complex suggest that there might be but a single species. Plants flower in spring and early summer.

Epithelantha F. A. C. Weber ex Britton & Rose 1922

Subfamily Cactoldeae, tribe Cacteae. Plants solitary to many-stemmed, extremely variable in size, spination, habit, and color. Stems depressed globose, 1-6 cm (0.4-2.4 in) in diameter, tuberculate, obscured by spines. Tubercles 1-3 mm long. Areoles small, at tubercle tips. Spines 19-38, in several series but not distinguishable as centrals and radials, white to light yellow. Flowers borne at the tips of young tubercles at the stem tips, bell shaped, white to pink, 3-12 mm (to 0.5 in) in diameter; pericarpels naked. Fruits club shaped, red, 3-18 mm (to 0.7 in) long, naked, indehiscent, with few seeds. Seeds oval, 1-1.5 mm long, shiny black, reticulate to papillate. Distribution: eastern Arizona, New Mexico, and west Texas, and Coahuila, San Luis Potosí, and Nuevo León, Mexico.

Epithelantha bokei L. D. Benson 1969 boke's button cactus

Plants almost always solitary, 2.5-5 cm ( 1-2 in) in diameter. Tubercles to 3 mm long. Spines in four or five series with about 10 inner and 25-28 outer ones, spreading, flattened against the stem surface, very dense, white, the longest to 4.5 mm. Flowers pink, 10-12 mm (0.4-0.5 in) long and in diameter. Fruits 3-9 mm (to 0.4 in) long. Distribution: restricted to the Big Bend region of west Texas, and adjacent

Mexico. Epithelantha bokei has been listed by the U.S. Fish 8c Wildlife Service as a proposed threatened species.

Epithelantha micromeris (Engelmann) F. A. C. Weber 1898

button cactus, mulatto, tapone

Mammillaria micromeris Engelmann 1856, Cactus micromeris (Engelmann) Kuntze 1891 Mammillaria micromeris [var.] greggii Engelmann 1856, Cactus micromeris [var.] greggii (Engelmann) J. M. Coulter 1894, M. greggii (Engelmann) Safford 1909, Epithelantha greggii (Engelmann) Orcutt 1926, £ micromeris subsp.greggii (Engelmann) N. P. Taylor 1998 Mammillaria micromeris var. unguispina Boedeker 1932, Epithelantha micromeris subsp. unguispina (Boedeker) N. P. Taylor 1998 Epithelantha densispina Bravo 1951, £. greggii var. densispina (Bravo)

Backeberg 1954 Epithelantha rufispina Bravo 1951, E. greggii var. rufispina (Bravo)

Backeberg 1954 Epithelantha spinosiorC. Schmoll 1951

Epithelantha bokei, also illustrated on page 81
Epithelantha micromeris subsp. greggii

Epithelantha pachyrhiza Backeberg 1954, E. micromeris subsp.

pachyrhiza (Backeberg) N. P. Taylor 1998 Epithelantha polycephala Backeberg 1954, £ micromeris subsp. polycephala (Backeberg) Glass 1998

Plants solitary to caespitose. Stems to 6 cm (2.4 in) in diameter. Tubercles 1-4 mm long, arranged in spiral series. Spines

20-26, variable, 1-2 mm long, white. Flowers whitish to pink, 3-10 mm (to 0.4 in) in diameter. Fruits 1.8-12 mm (to 0.5 in) long. Distribution: eastern Arizona, along the Rio Grande in New Mexico and west Texas, south into Coahuila, San Luis Potosí, and Nuevo León, Mexico.

The ethnobotanical use of Epithelantha micromeris is discussed in Chapter 2, under Cacti as Medicine. Five subspecies of E. micromeris are recognized. Subspecies micromeris is the smallest, neatest in appearance with strongly depressed stem tips, and the most northern; it occurs in eastern Arizona, New Mexico, west Texas along the Rio Grande, into neighboring Mexico. Subspecies greggii is large, to 5 cm (2 in) or more in diameter, and has a rough, somewhat bristly appearance. Spine color varies from chalky white to reddish brown. It is the most common subspecies in northern Mexico, especially around Saltillo, Coahuila. Subspecies pachyrhiza has tuberous roots and a stem only partly obscured by the white to orange-tan spines; it is found only to the southeast and northeast of Saltillo. Subspecies polycephala tends to form small clusters, the stems 1.5-2.2 cm (0.6-0.9in) in diameter. Spines number

21-27 and are all similar and whitish; it occurs in a limited area of Coahuila. Subspecies unguispina has a single series of black-tipped spines and tends to form clumps; it is found near Monterrey, Nuevo León, south into San Luis Potosí.

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