Annual or biennial, decumbent to 1 metre tall. Stems leaves, floral branches, flowers and fruit clothed in prominent succulent epidermal bladder cells; central stem erect with a leafy apex, 30–60(–100) cm tall, from which arise lateral floral branches in leaf axils; basal part of stem becoming somewhat woody up to 25 mm diameter; vegetative stems and floral branches at least basally distinctly angled-ribbed. Leaves opposite, decussate, petiolate, succulent, ovate-spathulate to lanceolate, (5.5)6–11 cm long, (1.8)3.5–4.5(–5.5) cm wide, mid green, paler or lower surface or reddish (exposed drier sites), with a slightly unpleasant scent. Floral leaves persistent. Flowers leaf-opposed; pedicels 20–30 mm long; receptacle 12–15 mm diam.; flowers (15–)40–70 mm diam.; sepals unequal, outer 2–3 larger, triangular to oblong-ovate, more or less triquetrous distally, lacking membranous margins, adaxial surface smooth, 9–12 mm long, the 2–3 inner smaller, similar in shape but with well-defined whitish membranous margins, 6–8 mm long; staminodes white, numerous, c. 180–220 exceeding sepals by 10–30 mm. Capsule (submature) hemispherical, 5–10 ribbed, 15–20 mm diam., succulent, red, prominently covered with epidermal bladder cells, glossy, mature capsules dehiscent, 10–15 mm diam., dry, straw-coloured; seeds pale brown, more or less triangular, c. 0.7–0.8 mm long, tuberculate. Flowers Nov.–Dec.(–Jan.)
MuM, MSB. Also naturalised SA, NSW. Native to southern Africa. In Victoria it is widespread in the Mildura region. It is common between Merrinee North and Merbein South along Sturt Highway and side roads, extending south to Red Cliffs, Thurla, and to the west side of the Raak Plain. It readily invades degraded roadsides, forming dense, extensive stands, with some populations extending for kilometres along roadsides. It also frequently invades remnant roadside native vegetation along roadsides and adjacent private land, and is a serious environmental weed. In constrast to M. crystallinum and M. nodiflorum which usually occur in inland and coastal areas, especially in Tecticornia-dominated habitats, M. guerichianum appears to prefer red brown sandy loam soils, appearing to avoid (at least for now) heavier soils.
Mesembryanthemum guerichianum differs from M. crystallinum in being an annual or a biennial, it's taller habit, presence of an erect central stem, broader stem diameter, stems are angled-ribbed, floral leaves are caducous, larger flowers, greater number of staminodes, and longer pedicels.
