Echinocereus is a genus of ribbed, usually small to medium-sized, cylindrical shaped cacti, comprising about 70 species native to the southern United States and Mexico in very sunny, rocky places. Usually the flowers are large and the fruit edible. The name comes from the Ancient Greek ἐχῖνος (echinos), meaning "sea urchin", and the Latin cereus meaning "candle". They are sometimes known as hedgehog cacti, a term also used for the Pediocactus and Echinopsis.

Description

The species of the genus Echinocereus grow solitary or branching with prostrate to erect shoots that are spherical to cylindrical. The roots are fibrous or bulbous. The plants reach heights of growth between 1 and 60 centimeters. On the tips of the 4 to 26 ribs, which are mostly clear and only rarely resolved into humps, are the areoles, from which differently shaped spines can arise. A distinctive characteristic and likely synapomorphy of the genus is the erumpent flowers. The floral buds develop internally and break through the epidermis of the stem. This flower morphology is likely an adaptation to protect the developing buds from low temperatures. Upon maturity, the flowers are usually brightly colored and open during the day. Echinocereus floral color is variable because perianth color reflects pollinator specificity. Red flowers are generally associated with hummingbird pollination, while pink flowers tend to correspond to moth pollination. Their pericarp and floral tubes are studded with thorns, bristles, and sometimes wool. The scar is usually green, but sometimes white in color. The spherical to ovoid fruits are green to red and mostly thorny. They are mostly juicy and open along a longitudinal slit. The sometimes fragrant fruits contain broadly oval, black, tuberous seeds 0.8 to 2 millimeters long.

Taxonomy

Echinocereus is a genus in the tribe Echinocereeae within the subfamily Cactoideae of the Cactaceae family. The Cactoideae can be further divided into two sister clades, Cactoideae I and II. Echinocereus is situated within the Cactoideae I clade within the Pachycereeae tribe, a tribe that represents a diversification that yielded columnar and arborescent forms. Echinocereus emerged 4.6 ± 1.7 million years ago. Echinocereus is a strongly supported monophyletic genus that is sister to Stenocereus, although there has historically been substantial debate about infrageneric classification because of the genus's high rates of morphological variation and convergent evolution.

Cultivation

Echinocereus spp. are easier to cultivate than many other cacti. They need light soil, a sunny exposure, and a fresh and dry winter to flower. They grow better in soil slightly richer than other cacti. In the wild, several of the species are cold hardy, tolerating temperatures as low as −23 °C, but only in dry conditions.

Species

The following species are recognized in the genus Echinocereus by Plants of the World Online: separated by sections established in Phylogeny in Echinocereus (Cactaceae) based on combined morphological and molecular evidence: taxonomic implications 2017.

Natural hybrids

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