Euphorbia Species, River Euphorbia

This is a columnar African species that can form thickets of spiny, impenatable plnat material. Common landscape plant in southern Calif...Read Moreornia but needs to be cut back frequently or gets to be a big mess. The other 'similar' species include Euphorbia trigona, and compact, extremely upright grower with much larger leaves and smaller overall size; Euphorbia angularis- also a smaller plant, but with very irregular and varying diameter along 'columns' and some degree of variegation- columns are very thin and somewhat rubbery in texture relative to E triangularis; Euphorbia grandicornis- a much larger plant with huge thorns and extremely variable 'columns/branches' in terms of shape and diameter; Euphorbia pseudocactus is not always 3-sided, and its smaller, with striking variegation and stout spines.... there are more, but those are the most commonly grown in cultivation here in the US that can be confused with E triangularis.

Many Euphorbias are 'triangular' in cross section and this species can be confused with these others just from the name. This one is a large species, eventually forming into a tree with a cylindrical woody trunk and large upright 'branches' that eventually get too heavy and collapse, either tearing off, or just hanging down. The ones that tear off have a tendency to root in place, and new plants, and a thicket, start that way.

Paired 1/2" spines project laterally and up, and are very sharp and thin, making this plant a danger to trim without gloves.

Leaves are 'tongue-like' and very small, showing up in wet times of the year when it's warm (late summer to fall in southern California if watered well... rarely if at all if not watered well) and show up at each spine, curling downward about 1cm.

Flowers are yellow-green and appear in fall.