Pincushion cactus [Greek coryph, head/helmet/crown, and Greek anthos, flower, referring to the apical location of flowers in contrast with the ring of lateral flowers in the related genus Mammillaria]

Allan D. Zimmerman & Bruce D. Parfitt

Mammillaria Haworth subg. Coryphantha Engelmann, Proc. Amer. Acad. Arts 3: 264. 1856 (as Mamillaria); Aulacothelae Lemaire; Cochiseia W. Earle; Cumarinia Buxbaum; Escobaria Britton & Rose; Escobesseya Hester; Lepidocoryphantha Backeberg; Neobesseya Britton & Rose

Plants erect, spheric and unbranched or, if branched, then ultimately forming low clumps or small mats. Roots diffuse, succulent taproots (sometimes tuberlike or massive), or in some species ultimately adventitious from bases of branches. Stems unsegmented, hemispheric, spheric, ovoid, or cylindric, sometimes flat-topped, tuberculate, 1-20(-50) × 1-15 cm after sexual maturity; tubercles conic to hemispheric or cylindric, never coalescing into ribs, protruding conspicuously, grooved on their adaxial (upper) sides in sexually mature plants, i.e., areoles of sexually mature plants each consisting of fertile meristem (often woolly) in tubercle axil and spine cluster on tubercle apex, the two connected by a linear isthmus (areolar extension, often short woolly) recessed into an areolar groove on adaxial side of tubercle (groove extends only ¹/2-³/4 distance from spine cluster to tubercle axil in C. macromeris); areolar glands present or absent; cortex and pith usually mucilaginous or with mucilage confined to flowers and fruits. Spines 3-95 per areole, color various, needlelike (peglike in C. minima), usually differentiated into radial and central spines; radial spines straight or curved; central spines, when present, straight or curved (hooked in C. robustispina), terete, 4-55 mm. Flowers diurnal (sometimes ± vespertine in C. tuberculosa), borne at or near stem apex (lateral in C. recurvata), on new growth of current year and/or last-produced areoles of preceding year (fruiting zone in some species becoming displaced outward and downward by apical vegetative growth after flowering), campanulate or funnelform to nearly salverform with recurved tepals, 1-6.5 × 0.6-10 cm; outer tepals entire or fringed; inner tepals variously colored, never pure red or blue, 4.5-40 × 1-15 mm, often glossy, margins entire, toothed, fringed, or erose; scales on ovary none or few, narrow or rudimentary, entire or erose, axils naked, spineless; stigma lobes 4-13, white to yellow or orange-yellow (rarely pinkish), 0.5-8 mm. Fruits indehiscent, green or red, spheric, ellipsoid, ovoid to narrowly fusiform, or obovoid, 1.5-50 × 1.5-20 mm, usually juicy, sometimes slimy or fleshy (dry in C. minima), scales usually absent (or few), spines absent; pulp colorless to white, greenish, or pinkish; floral remnant persistent or deciduous. Seeds usually reddish brown or black, sometimes yellowish, reniform, comma-shaped, obovoid, or spheric, 0.8-3.5 mm in greatest diam., shiny or glossy; testa smooth, raised-reticulate, or pitted; strophiole (unsclerified tissue in/around hilum) small or large, flat or slightly protruding, never surrounding micropyle, replaced by a narrow raphe in some species (e.g., C. ramillosa); sclerified collar between hilum and micropyle short, solid or grooved, nearly open in some species. x = 11.

Species 60-70 (20 in the flora): w North America, Mexico, West Indies (Cuba).

Coryphantha may be polyphyletic, or paraphyletic, with respect to Mammillaria, from which it differs primarily by the presence of an adaxial areolar groove on tubercles of sexually mature coryphanthas. Most species of Coryphantha produce a more or less apical tuft of flowers from the current growth; most mammillarias bloom in a ring from older areoles at least 1 cm from the stem apex. Coryphantha recurvata is an exception with a ring of flowers as in most species of Mammillaria. Some species in each genus display intermediate floral positions. In both genera, pitted seeds characterize putatively primitive species.

The coryphanthas with pitted seeds often are segregated as Escobaria (species numbered 8-20 here). That segregate, recognized by the International Cactaceae Systematics Group (ICSG) but not here, lacks the glands found in the areoles of typical Coryphantha. Such glands are ephemeral. The glands, occuring singly or in small groups usually at either end of each areolar groove, are spheroid or mushroom-shaped (then deeply nestled among short trichomes so appear to be hemispheric), smooth, colorful (red, green, purplish, orange, or yellow), and about 1 mm in diameter. Fallen glands leave circular gray scars.

Several species of Coryphantha closely resemble, and may be confused with, Neolloydia conoidea. Both genera have naked ovaries and grooved tubercles; however, Neolloydia has seeds like those of Ariocarpus or Lophophora. The tiny fruits of N. conoidea usually are overlooked, often leading to misidentifications. In immature plants of several genera that tend to be "ribbed" (e.g., Echinomastus), and in the adults of neotenous species, stems are tuberculate; however, the areolar extensions in those plants are shorter and/or wider than those of Coryphantha, and the tubercles usually are basally confluent, unlike the (linear) grooves and distinct tubercles of Coryphantha and Neolloydia.

As many as fourteen species of coryphanthas may occur sympatrically, with no natural hybrids dectected. Flowers may be few and ephemeral; however, identifications based on vegetative traits may be difficult because of polymorphism and age-related heteromorphic growth within populations, geographic variation within species, and parallel evolution among ecological counterparts in relatively distant lineages.

Calcium oxatate crystal aggregates (druses) in the stem parenchyma of Coryphantha are spheric, oblong, or lens-shaped masses like grains of sand. Most druses are only 0.1-0.4 mm diam., seen best with a compound microscope and polarizing filters, but five species (species 16-20) have unusually large druses (0.5-1 mm diam.) conspicuous to the naked eye. With practice, the thick pale-looking skin associated with a several-layered and/or druse-containing stem can be recognized.

Species with specialized mucilage cells in the pith and cortex of stems are wet with tangibly and visibly viscous slime when cut open. Mucilage usually can be seen and felt in healthy living tubercles. Fresh sections feel watery or mealy in species lacking specialized mucilage cells.

A medullary vascular system (when present) is a diffuse network of fine threadlike strands of wood inside the pith at the center of the stem, within the woody vascular cylinder. Such whitish vascular strands are seen by holding a light source behind a translucently thin stem section.

Stem diameter includes the tubercles, unless otherwise stated; lesser stem diameter excludes the tubercles and is used only to define the relative size of the pith. Tubercle diameter is the maximum measurement of the cross section at midpoint between the base and apex of a tubercle. Spine thickness is measured midspine.

Flower length may be misinterpreted on flowers deeply hidden in the axils of the subtending tubercles. Accurate measurements of diameter require fully opened flowers (in some species the flower may not be fully open if the angle between the inner tepals and floral tube is less than 45º). Fruits with fully formed seeds may not be mature with respect to taxonomically important characters of fruit size and color. Ripe fruits are those that abscise easily from the plant with a gentle tug (although fruits of Coryphantha robustispina sometimes require a hard pull). A pitted seed testa is easily viewed with a hand lens. A weakly raised-reticulate seed testa is distinguishable from a smooth testa only with a lens (10× or greater magnification). A reticulate color pattern alone does not imply that the anticlinal cell walls actually protrude.

SELECTED REFERENCES

Taylor, N. P. 1983. Die Arten der Gattung Escobaria Britton et Rose: [1]-5. Kakt. And. Sukk. 34: 76-79, 120-123, 136-140, 154-158, 184-188. Zimmerman, A. D. 1985. Systematics of the Genus Coryphantha (Cactaceae). Ph.D. dissertation. University of Texas.