This annual grows on light soils in dry places. Its natural habitat is dry, rocky, calcareous grassland on chalk and limestone. However, it is more frequent in artificial habitats such as abandoned arable fields, quarries, old walls, trackways, railway banks and sidings. Mainly lowland, but reaching 400 m at Langcliffe in the Craven Pennines (Mid-W. Yorks.).
This tufted, calcifugous perennial herb grows in thin humus in dry narrow cracks in slabs of siliceous rocks of Old Red Sandstone age. 510-610 m in the Caha Mountains (S. Kerry and W. Cork).
This cushion-forming montane perennial herb is always associated with strongly base-rich rocks, including limestone and soft calcareous schists. The vegetation is usually open, as the ground on which it usually grows is both easily eroded and subjected to frost-heave. It reaches an altitude of 1180 m on Ben Lawers (Mid Perth), and formerly descended to 120 m on Unst (Shetland).
M. sedoides is a mat- or cushion-forming perennial herb of base-rich rocks, flushed grassland, exposed montane heath, and mountain ledges and plateaux. From 335 m on Skye (N. Ebudes) to 1200 m on Ben Lawers (Mid Perth), but has been recorded at 215 m washed down in the stony bed of the R. Fillan at Tyndrum (Mid Perth).
A loosely tufted but slender perennial herb that has only ever been known in Britain from Widdybank Fell, where it grows in open, gravelly flushes and eroding margins of sikes on metamorphic sugar limestone. The plant is not a strong competitor and is mainly associated with hummock-forming mosses and species such as Carex capillaris, Juncus triglumis, Minuartia verna and Primula farinosa. Upland, from 490 to 510 m on Widdybank Fell (Co. Durham).
M. verna is a perennial, basicolous, cushion-forming herb, characteristic of Carboniferous limestone districts where it is found in short grassland, on scars, on limestone pavement and scree. It also grows on base-rich volcanic rock in N. Wales and basalt in N. Ireland, on metal-rich soils, including those derived from serpentine, and on mining spoil. It prefers open sites with reduced competition, but may suffer from drought in very exposed conditions. Although seldom above 600 m, it has been recorded at 875 m on Snowdon (Caerns.).