Homalocephala texensis

A stem close to the ground surface

Homalocephala texensis (formerly Echinocactus texensis) usually grows singly. In younger and deeply set specimens, a broad, flattened apex is visible above ground. An older stem may become hemispherical. Distinct ribs have sharp edges and widely separated areoles, leaving the green surface between spines clearly visible. [Zimmerman and Parfitt 2003a]

Britton and Rose highlighted the broad central spine, distinctly flattened and marked with transverse rings. Shorter radial spines grow around it. In their historical description, the spines were reddish, while the flora of North America account presents a broader variation from light brown and pinkish to grey. Small, flattened hairs on spine surfaces can be recognised under magnification. [Britton and Rose 1922] [Zimmerman and Parfitt 2003a]

Range and habitat variation

According to POWO, the native range extends from southwestern Oklahoma to northeastern Mexico and also includes New Mexico and Texas. Flora of North America lists the Chihuahuan Desert, grasslands, openings in oak woodland and Tamaulipan thornscrub. Plants have been found both on deeper soils of plains and on low limestone hills. [2-WWW] [Zimmerman and Parfitt 2003a]

The broad range is associated with variation in appearance. In western desert populations, stems are more grey-green, and central spines are longer and project more strongly. Plants from the eastern part of the range usually have greener stems. The low habit means grasses and other seasonally growing plants can conceal a specimen entirely. In this position, its sharp spines lie close to ground level. [Zimmerman and Parfitt 2003a]

A flower opening in sunlight

The flower has pink to nearly white tepal tips and an orange or red region at their bases. Inner tepal margins are finely and irregularly fringed. Narrow scales with sharp tips cover the lower flower portion, and tufts of white hairs develop in their axils. Perianth colour and margin structure are useful characters when comparing flowering plants. [Britton and Rose 1922]

The monograph from 1922 described flowers opening in full light over four successive days and closing at night. The authors also mentioned a delicate scent. This is a phenological observation recorded in the historical account, consistent with the species’ daytime flowering rhythm. [Britton and Rose 1922]

The red fruit and variation in ripening

The mature fruit is globular or ovoid, red and fleshy. Its hairs become sparser than on the developing flower base, leaving the surface clearly visible. The black seeds are smooth and shiny, with a large, sunken funicular scar. The combination of a juicy fruit and pink flower distinguishes the species from H. parryi and H. polycephala. [Britton and Rose 1922] [Vargas-Luna et al. 2018]

Britton and Rose also described differences among fruit lots. Some gradually dried and split irregularly, while large fruits sent to them from Texas in 1921 remained closed during ripening. The newer flora treats fruits primarily as indehiscent, with rare irregular rupture. The different descriptions reflect variation in fruit ripening, with fleshy tissues retained for some time. [Britton and Rose 1922] [Zimmerman and Parfitt 2003a]

Position in the classification

Britton and Rose established Homalocephala specifically for this species, combining stem, flower, fruit and seed characters. The molecular and morphological analysis from 2018 placed it in a shared lineage with H. parryi and H. polycephala, separate from Echinocactus. The earlier name remains a key to the literature, while the current combination expresses the relationship treatment adopted in the atlas. [Britton and Rose 1922] [Vargas-Luna et al. 2018] [2-WWW]

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b, file p. 7] [Neciu b.d., file p. 1] [U.S. Fish and Wildlife Service 2003, file p. 13]