‘Snow on the mountain’ is an annual herb.
Growing from a taproot they are around 80 (150) cm high and can be up to 40 (30 to 50) cm wide.
Plants can be a single stem or the upper part may be branched and bushy.
The green stems may become brown or reddish in older plants.
Stems on young plants have dense white hairs but these disappear with age.
Parts exude a milky latex when damaged.
The lower or stem leaves are alternate with stipules under 1 mm long.
They have no petiole or one a few mms long with a few hairs on it and the blade base.
The blades are up to 9 cm long and 2.5 to 3 cm wide.
They are ovate, obovate or elliptic with a rounded base and a sharply pointed tip.
They are a pale to mid green and the edge may be wavy.
Inflorescence leaves, in the distal branches are opposite or whorled.
They are narrower than the stem leaves and have a white border.
The branched terminal inflorescences are a single cyathium (‘flower’) or a small cluster.
Each cyathium is on a hairy peduncle around 2 to 2.5 cm long.
At the base of the peduncle is a leafy bract with a wide white border or is all white.
The cyathia are typical of the Euphorbiaceae.
The green bell or cup-shaped involucre, around 3 mm long is covered in white hairs.
Between the 4 or 5 deeply fringed involucral lobes are the nectiferous glands.
The kidney-shaped to almost circular glands are around 1 to 1.5 mm long.
They are greenish yellow and depressed in the centre.
Each gland has a white petal-like appendage up to 4 mm long.
Inside the involucre are many staminate or male flowers that have no sepals or petals.
Each consists of a single stamen with long, linear and hairy bracteoles at the base.
The female flower is a single carpel on a pedicel.
The ovary is covered in dense long white hairs.
Each of the 3 locules has a single ovule.
There are three 2.5 mm long styles divided from half to two-thirds of their length.
The ovary can be erect or drooping and the pedicel lengthens as the fruit grows.
The fruit are 3-lobed capsules up to 6 mm long covered in white hairs.
The 3 to 4 mm long seeds are almost circular or ovoid.
The surface may be smooth or wrinkled or be covered in small bumps or tubercles.