Euphorbia perrieri, Drake, 1899

Haevermans, Thomas & Hetterscheid, Wilbert L. A., 2021, Taxonomic changes and new species in Malagasy Euphorbia (Euphorbiaceae), Phytotaxa 492 (1), pp. 1-61 : 31

Key:—Species of the informal Euphorbia perrieri group

1. Cyathia and cyathophylls facing upwards, plant profusely producing stems from the base...................... Euphorbia multibrachiata

- Cyathia and cyathophylls nodding, plant unbranched or infrequently branching along the main stem ...........................................2.

2. Plant at most 1 m high, base swollen, globose or oval, with usually one stem, thin (to 1.5 cm in diam.,) unbranched or with a few branches near the top, main stem largely (at least the lower half) devoid of spines ..................................... Euphorbia perrierioides

- Plant up to 2 m high, base not swollen, main stem thick (2–5 cm diam.), unbranched or with a few branches, with spine remains all over or at the most missing from the lower 10 cm .......................................................................................................................3.

3. Spines arranged in regular helical rows, spine bases swollen, more or less laterally flattened, entire or rarely with 1–3 small, accessory spinules on the base, non-swollen top of the spine very short, remaining with age, leaves petiolate, narrowly ellipticalobovate ................................................................................................................................................................ Euphorbia paulianii

- Spines arranged in often irregular helical rows, often partly unordered, spine bases usually or a majority with several accessory small spinules on the base, spine base swollen, top part at least as long as the basal swollen part, thin, caducous, leaves sessile or almost so, elliptical................................................................................................................................................ Euphorbia perrieri