The genus Echinopsis, as circumscribed following modern molecular revisions, is one of the most diverse in the Cactaceae family, encompassing both small globose cacti and towering columnar species previously classified in the genus Trichocereus. A member of the subfamily Cactoideae, Echinopsis is distributed across South America from Bolivia and Peru south to Argentina and Chile. The genus is celebrated by cactus enthusiasts for its remarkably large and spectacularly coloured flowers, which appear in great profusion even on relatively small plants.
Classification and nomenclature
The genus Echinopsis belongs to the order Caryophyllales, family Cactaceae, and subfamily Cactoideae. It was first described by Johann Heinrich Zuccarini in 1837. In recent decades, comprehensive molecular phylogenetic studies have led to the synonymisation of Trichocereus — a genus of large columnar cacti — within Echinopsis, substantially enlarging its circumscription. The resulting genus thus spans an extraordinary range of growth forms, from diminutive globose plants to tree-sized columnar specimens.
Morphological description
Habit and dimensions
The diversity of form within Echinopsis reflects its enlarged modern circumscription. The original small-growing globose species (e.g. E. eyriesii, E. oxygona) form solitary or clustering balls rarely exceeding 30 cm in height, whilst the former Trichocereus species (e.g. E. pachanoi, E. terscheckii) are fast-growing columnar cacti reaching 6–12 metres. The intermediate species (E. spachiana) form multi-stemmed clumps of erect columns to 2 metres.
Stems and areoles
Stems are ribbed, with the number of ribs ranging from 8 to 20 depending on the species. Areoles bear both radial and central spines; these vary from hair-like and inconspicuous to stout and brownish. In the larger columnar species, the areoles are spaced along the rib crests and produce abundant offshoots from the base, facilitating vegetative propagation. The skin is smooth and green to blue-green.
Flowers
The flowers of Echinopsis are truly spectacular: large, funnel-shaped, and produced in profusion from lateral areoles. They range in colour from pure white to pink, red, orange, yellow, and intermediate shades, depending on the species. In the original small-growing species, flowers are typically white and nocturnal, emerging at dusk and lasting only one night; in the columnar species, flowers are more often diurnal or bimodal. The floral tube is long and hairy in many species.
Fruits
Fruits are fleshy, globose to ovoid berries, covered with hair and bristles, maturing to green, yellow, or reddish. They contain numerous small black seeds within a white or pinkish pulp. The fruits of columnar species, particularly E. pachanoi and E. terscheckii, are edible and consumed locally in the Andes.
Distribution and habitat
Echinopsis species are found across a wide range of habitats in South America. The smaller globose species occupy rocky hillsides and grasslands at lower to moderate elevations in Bolivia, Argentina, and Brazil. The columnar species are native to the Andean slopes and inter-Andean valleys of Peru, Bolivia, and Argentina, often growing at altitudes of 1,000–3,000 metres in montane scrub and on rocky outcrops. Echinopsis pachanoi is particularly associated with the cloud forests and high valleys of Ecuador and Peru.
Main species
Echinopsis pachanoi — the San Pedro cactus; a fast-growing columnar species from Peru and Ecuador, reaching 6 m; widely cultivated as an ornamental, also of cultural and historical significance in Andean traditions.
Echinopsis spachiana — a clustering columnar species producing slender, bright green stems to 2 m; one of the most commonly used rootstocks for cactus grafting.
Echinopsis terscheckii — the cardón grande of Argentina; a towering tree cactus reaching 12 m with stout spines and large white flowers; prominent in Argentine dry forests.
Echinopsis oxygona — a freely clustering globose species bearing very large pink flowers; one of the most floriferous members of the genus in cultivation.
Echinopsis eyriesii — a classic species with globose to short-cylindrical stems bearing white nocturnal flowers of outstanding size; widely grown since the early nineteenth century.
Cultivation
Climate and exposure
Echinopsis species are amongst the most rewarding cacti in cultivation, flowering generously even as young plants. Full sun is preferred; in climates with mild winters, the larger columnar species make excellent garden subjects. The small-growing species are ideal for pot culture and windowsill collections, producing their spectacular flowers with little special attention.
Substrate and watering
A free-draining compost, amended with grit or perlite to prevent waterlogging, suits all members of the genus. Watering should be generous during the growing season; the plants signal dehydration by slight wrinkling of the stem. Allow the substrate to dry thoroughly between waterings. Reduce water considerably in late autumn and keep plants dry through winter.
Cold hardiness
Cold hardiness varies with species and provenance. High-altitude Andean species such as E. terscheckii and E. pachanoi are considerably hardier than might be expected, tolerating light frosts if kept dry; they may survive temperatures of −5 to −8 °C. Lower-altitude and Brazilian species are generally more cold-sensitive. Greenhouse or frost-free indoor overwintering is recommended in climates with prolonged or severe frosts.
Conservation
Several Echinopsis species, particularly the large Andean columnar cacti, face pressure from agricultural expansion, logging of dry forests, and illegal collection for the horticultural trade. Echinopsis pachanoi is subject to CITES regulations, and wild collection is prohibited without authorisation. Cultivated plants are readily obtainable and should always be preferred over wild-sourced material. The genus as a whole benefits from active cultivation by enthusiast collections worldwide, which maintain genetic diversity outside of natural populations.