Oehmea sphacelata

Name and subspecies

The current name Oehmea sphacelata (Mart.) Guiggi was formed by transferring Mammillaria sphacelata Mart. to Oehmea in 2022. Older accounts also contain combinations in Neomammillaria, Leptocladodia and Escobariopsis. POWO accepts two subspecies, O. sphacelata subsp. sphacelata and O. sphacelata subsp. viperina (J.A.Purpus) Guiggi. Both are described in this account, retaining their distinct characters. [2-WWW] [Guiggi 2022, POWO, as of 11 October 2026. Guiggi, p. 2]

Stems, tubercles and spines

The Tehuacán-Cuicatlán valley flora describes stems branching from the base or middle, globose to cylindrical, erect, decumbent or creeping. Across the regional material, they reach 3–20 cm in height or length and 1.5–4 cm in diameter. The sap is watery. The light green, shortly cylindrical tubercles are 3–8 mm long and 3.5–6 mm wide at the base. Tubercle axils are glabrous or contain a few white bristles. [Arias et al. 2012, p. 115]

The radial spines are needle-like, straight or slightly curved, 3–9 mm long, ranging in colour from white and yellowish to brown, often with a darker tip. Central spines are straight, directed upwards and lack a hooked tip. They are usually 4–6 mm long, sometimes up to 9 mm. Spine counts differ distinctly between subspecies. [Arias et al. 2012, p. 115]

In the regional diagnosis, the nominate subspecies has stems 4–20 cm high and 3–4 cm in diameter, eight to fifteen radial spines and one to four central spines. Subsp. viperina has thinner cylindrical stems, 3–15 cm long and 1.5–2.5 cm in diameter, eighteen to twenty-four radial spines and six to ten central spines. These combined structural characters help compare material identifications. [Arias et al. 2012, p. 115, 117]

Flowers, fruits and seeds

The flowers are funnel-shaped, most often 1.5–2 cm long, sometimes from 1.1 cm. The inner tepals are purple to red, lanceolate or narrowly lanceolate. The outer tepals are dark green with a purple central stripe. The style is pink, and the stigma has three to five green lobes. The red, club-shaped fruits are 0.8–2 cm long and 0.3–0.6 cm wide. Seeds reach 1–1.5 mm in length and about 0.8 mm in width, with a black coat. [Arias et al. 2012, p. 115]

The regional flora reports flowering from October to April for both subspecies. This period describes populations in the Tehuacán-Cuicatlán valley. The precise sequence of flowering in individual plants depends on local conditions, which this floristic description does not quantify separately. [Arias et al. 2012, p. 117, 119]

Range and habitats

The species is endemic to Mexico and known from Puebla and Oaxaca. Material in the regional account comes from the Tehuacán-Cuicatlán valley and its hills. Both subspecies occur on calcareous substrates in oak forests, tropical forests that shed their leaves in the dry season, and xerophytic scrub. The reported elevation range is 900–2100 m above sea level. Descriptions were based on herbarium specimens and field locations listed in the flora. [2-WWW] [Arias et al. 2012, p. 115–119]

Significance for phylogeny

In 2021, Breslin and colleagues placed this species, studied as Mammillaria sphacelata, at the base of the Coryphantha clade. They noted that its morphological group has tubercles without the longitudinal groove on the side facing the stem apex that is characteristic of typical Coryphantha. Sampling other species in this group was intended to resolve how to connect plant structure with clade boundaries. [Breslin et al. 2021, p. 312–316]

The name change to Oehmea sphacelata allows this problem to be followed in the current classification. Diagnoses in older floras under the name Mammillaria sphacelata remain sources of structural and habitat data. Proposals to expand Oehmea in 2026 are discussed alongside the scope of available analyses in the taxonomic article. [2-WWW] [Breslin and Majure 2026]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Anonim b.d.aa, file p. 1]