Origin and Habitat: Rio Negro region in Southern Argentina.

• Echinopsis melanopotamica Speg.

• Echinopsis leucantha (Gillies ex Salm-Dyck) Walp.
• Cereus leucanthus (Gillies ex Salm-Dyck) Pfeiff.
• Echinocactus leucanthus Gillies ex Salm-Dyck
• Echinonyctanthus leucanthus (Pfeiff.) Lem.
• Trichocereus shaferi Britton & Rose non Britton & Rose
• Echinopsis campylacantha Pfeiff. & Otto
• Echinopsis campylacantha var. leucantha Labour.
• Echinopsis campylacantha var. stylodes Monv.
• Echinopsis cordobensis Speg.
• Echinopsis gladispina Y.Itô
• Echinopsis incurvispina (Otto & A.Dietr.)
• Cereus incurvispinus Otto & A.Dietr.
• Echinopsis intricatissima Speg.
• Echinopsis leucantha var. brasiliensis Speg.
• Echinopsis leucantha var. volliana Backeb.
• Echinopsis melanopotamica Speg.
• Echinopsis spegazziniana Britton & Rose

Description: Echinopsis melanopotamicaSN|11363]]SN|8250]] which comes from the Rio Negro region in Southern Argentina represent the southern form of Echinopsis leucanthaSN|21017]]SN|8246]].
Similar species: It is related both with Echinopsis rhodotrichaSN|8246]]SN|21017]] and Echinopsis feroxSN|8250]]SN|11363]]. But it is easily recognizable for its cylindrical stem and upper spines bent over the plant apex.
Habit: Plants solitary for a while but eventually may form clumps.
Stem: Globose to oblong, 25-100(130) cm tall.15-25 cm in diameter. Very dark green sometime greyish or purplish.
Ribs: 12-14, obtuse, somewhat compressed up to 1,5 cm tall.
Areoles: Close together, oblong.
Radial spines: About 6-8, orangish-yellow to dark brown, subulate, rigid, with a bulbous base, more or less curved, 1-2 cm long.
Central spines: 1 strong, curved, elongated, usually 3 cm long (but often up to 10 cm long)
Flowers: Funnel-form, up to 16 (or more) cm long, 10 cm in diameter, the tube about 3 cm broad at the mouth, dark brown, with scattered areoles bearing small tufts of brown hairs. Outer perianth segments brownish, spreading, 2 cm long, with an acute scarious tip. Inner perianth segment in about 3 series, spreading, the outer purplish, the inner ones white, oblong, acute approx 3 cm long. Filaments many of unequal length, the series at the mouth of the flower-tube erect up to 1,5 cm long. Stigma lobes numerous creamy-white to green.
Fruits: Orangish, dehiscent, pulp white.
Seeds: Black, up to 1,5 cm in diameter.

Bibliography: Major references and further lectures
1) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” Courier Dover Publications, 1963
2) James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass” Cambridge University Press, 11/Aug./2011
3) David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006 ISBN 0953813444, 9780953813445.
4) Edward F. Anderson “The Cactus Family” Timber Press, 2001
5) Clive Innes, Charles Glass “Cacti” Portland House, 01/May/1991
6) Méndez, E., Ortega-Baes, P. & Kiesling, R. 2013. Echinopsis leucantha. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 31 March 2015.

Cultivation and Propagation: The Echinopsis melanopotamicus is a summer grower species that offers no cultivation difficulties. Water regularly in summer (but do not overwater ) needs good drainage and very porous soil, keep rather dry in winter. Feed with a high potassium fertilizer in summer. It is quite frost resistant if kept dry (hardy to -10° C). Need a bright exposure, full sun or half shade in summer.
Propagation: Direct sow after last frost, offsets.