Annual Knawel

Scleranthus annuus is an annual or biennial herb with low, much-branched spreading stems up to 15 cm (6 in) long growing from a taproot. The leaves are needle-like or linear in shape with sharp, stiff points. They are oppositely arranged in pairs about the stem and are fused together at the bases. Flowers occur in pairs or small clusters of up to five. The flowers lack petals but have bell-shaped calyces of green petal-shaped sepals.

It grows in soil pockets among rocks, on bare places, on disturbed sandy soil on heaths, in arable fields, in sand pits, in quarries, and occasionally on shingle on the coast or beside rivers.

The plant seems to have three different life strategies; some seeds germinate in the autumn and overwinter as small seedlings; others overwinter as seeds and germinate in the spring, flowering the same year; and some germinate in the spring but do not flower until the following year. The flowering period for all three groups extends from late May to late August. The flowers make little effort to attract insects for pollination (no showy petals, little nectar), and most are self-pollinated.