Coryphantha
Coryphantha is a genus of roughly fifty species of small, globular to short-cylindrical cacti native to Mexico and the southwestern United States. The name comes from the Greek for "top-flowering" — a reference to the way the large yellow, pink or magenta flowers open from the very crown of the plant, nestled among prominent, grooved tubercles rather than along the ribs. Closely related to Mammillaria, Coryphantha is distinguished chiefly by a groove running along the upper surface of each mature tubercle.
Description
Coryphantha species are ribless cacti whose bodies are built up instead from spiralling ranks of firm, conical to cylindrical tubercles. The defining feature of the genus is a narrow groove running from the spine-bearing tip of each mature tubercle back toward its base; this groove is where flowers are produced, and it often carries a line of wool or a small nectar-secreting gland. Younger, non-flowering tubercles near the growing point may lack a fully developed groove.
Most species are solitary when young, though many clump with age to form low mounds. Spines are borne in radiating clusters at the tubercle tips, ranging from short and comb-like to stout and curved depending on the species, and are frequently accompanied by contrasting central spines. The flowers are comparatively large and showy for the size of the plant — typically funnel-shaped, satiny, and yellow, though pink, magenta and red-throated forms occur — and open at the apex of the plant in spring and summer. Small, greenish to yellowish fruits follow, ripening more or less hidden among the tubercles.
Distribution and habitat
The genus is centred on the arid and semi-arid uplands of Mexico, with a number of species extending north into Texas, New Mexico, Arizona and neighbouring parts of the United States. Plants grow in grassland, desert scrub and rocky limestone or gravel slopes, often tucked among low vegetation or wedged into crevices where they gain some shelter from grazing and the harshest sun. Many species contract into the ground during drought and cold, so that little more than the flat top of the plant is visible for much of the year.
Notable species
- Coryphantha elephantidens — a large, plump Mexican species with broad tubercles and big pink to cream flowers; a favourite in collections.
- Coryphantha cornifera — noted for its stout, horn-like central spine and clear yellow blooms.
- Coryphantha macromeris — the "nipple beehive cactus", forming clumps of long, soft tubercles across the US–Mexico borderlands.
- Coryphantha pycnacantha — a densely spined Mexican species with golden flowers.
- Coryphantha maiz-tablasensis — a small, geographically restricted species of conservation concern.
Cultivation
Coryphantha are generally undemanding for growers who respect their need for sharp drainage and a genuine winter rest. Pot them in a gritty, mostly mineral mix and give them the brightest position available; strong light keeps the tubercles compact and encourages the heavy spination that makes many species attractive. Water thoroughly through the warm growing season once the soil has dried, then reduce sharply as autumn arrives — see Watering for general timing.
A cool, dry, more or less frost-free winter rest is important: it lets the plants contract naturally, hardens them against rot, and is generally necessary to trigger the following season's flowers. The taprooted or fleshy-rooted habit of many species means they resent sitting in cold, wet compost, so err on the side of underwatering out of season. Repot young plants every year or two to refresh the medium; see Repotting.
Propagation
Seed is the usual and most reliable method for the genus, and the way to raise most species true. Sow onto a warm, mineral surface kept humid until germination, then grow the seedlings on gradually — see Propagation — seed. Clumping species can also be increased by detaching rooted offsets once they are large enough to handle, allowing the cut surface to callus before potting. Choice or slow-growing plants are sometimes grafted to speed them along, though most Coryphantha grow perfectly well on their own roots.
Common problems
- Rot — the most frequent killer, almost always from overwatering, a poorly draining mix, or watering during the cold winter rest.
- Etiolation — too little light causes soft, elongated growth and weak spination, spoiling the plant's natural symmetry.
- Pests — mealybugs (including root mealybugs on the fleshy roots) and red spider mites are the usual offenders; see Pests and diseases.
- Failure to flower — usually traced to a warm or overly wet winter; a proper cool, dry rest is the remedy.
See also
- Mammillaria — the closely related, ungrooved-tubercle genus often confused with Coryphantha
- Escobaria — another grooved-tubercle relative
- Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases