Coryphanthas are small to medium-sized globose to short-columnar tubercled cacti from Mexico and the south of the USA, which grow in dry regions and deserts between the Sierra Madre Oriental and the Sierra Madre Occidental. The plant bodies are not partitioned into ribs as e.g., in Ferocactus, Thelocactus etc., but into tubercles as in the closely related genus Mammillaria.
The name Coryphantha originates from the Greek koryphe = apex and anthos = flower and means "flowering from the apex". The flowers are quite large (3-10 cm diameter) and arise from the new growth,which is in the centre of the plant, contrary to e.g. Mam-millarias, which flower around the top from the growth of the year before. The flowers often are yellow, but also white or pink. The fruits are green and juicy, with attached flower remnants, the seeds are mostly reni-form, brown, with reticulate testa structure.
The tubercles of Coryphanthas have a groove on their upper surface which usually reaches from the spine-bearing areole to the axil. The flowers originate from this groove, from which the plants may also sprout. Different types of areole development exist, which gives hints about the possible developmental history of the genus (phylogenesis).
In some species in these grooves and/or the axils, so-called nectary glands are produced which are mostly yellow, orange or red and which produce a sugar-containing sap. This sap may serve to attract ants, which, by their marking, keep plant- and mainly bud-eating animals from the plant.
The genus is characterised by the following three features, which should be present in adult plants:
1. Flowers in the apex of the plant.
2. Flowering tubercles grooved.
Each cactus with tubercles showing these three features belongs to the genus Coryphantha. Moreover, all Coryphanthas have the potency to produce extrafloral nectary glands.
Following this definition and mainly due to the seed morphology, the following species have to be separated from Coryphantha: all species of the genus Escobaria which show foveolate testa cells and Cumarinia, with channelled anticlinal boundaries.
Coryphanthas belong to the slow-growing cacti and often are floriferous only after 8-10 years. Formation of a tubercle groove indicates that a plant has become floriferous. Many species pass through several stages, in which they change their appearance repeatedly. In nature, slow growers are heavily influenced by the microclimate at their individual location and, therefore, are surprisingly variable. These are also the main reasons, why up to now, more than 300 supposedly different species or combinations have been published which, as a result of our studies, must be reduced to 43 species and 11 subspecies.
For a better understanding of the genus Coryphantha, in addition to their great variability in nature, three particularities must be considered:
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