Journal archives for August 2017

August 13, 2017

Euphorbia marginata (Snow-on-the-Mountain) and E. bicolor (Snow-on-the-Prairie)

I recently went through E. marginata and E. bicolor and found some characters that might help those trying to distinguish between the two snowy plants.

Euphorbia marginata:

Upper sides of most or all leaves glabrous (occasionally hairy on lower leaves, especially along the midvein). Bracts broad, largest ones typically elliptic with the broadest point near the middle. Smaller bracts becoming oblong or even oblanceolate with the broadest point at the apex, as long or typically shorter than the rest of the leaves.

The bracts are typically the same length as or shorter than the rest of the leaves, but can occasionally get to 1.5 or maybe even 2 times the length on occasions. These extra long leaves are quite broad and closely resemble the actual leaves in shape and size despite the white margins.

Image source: Nathan Taylor

More examples:
Young growth (no inflorescence)
Young inflorescence 1
Young inflorescence 2
Inflorescence with narrow bracts

Euphorbia bicolor:

Upper sides of leaves hairy (and often densely so). Bracts long and narrow, largest ones typically linear or narrowly oblanceolate with the broadest point at or near the apex. Smaller bracts linear or if approaching oblanceolate, then longer than the regular leaves.

The bracts that seem to be in transition from the leaves are often oblong but are typically shorter than the more apical linear to narrowly oblanceolate bracts.

Image source: Lisa Winnett-Pequeno

More examples:
Young growth (no inflorescence)
Young inflorescence
Rare pink form

This is adapted slightly from Flora of North America, but their treatment says that the leaves of E. marginata are glabrous in the key when in actuality they can be densely hairy, though not on the upper surface and typically most restricted to the midvein. I hope this helps.

Posted on August 13, 2017 02:10 by nathantaylor nathantaylor | 15 comments | Leave a comment