This plant is not found fossil in any deposits. It is found in Arctic Europe, North Africa, and Western Asia. In Great Britain it is absent from S. Somerset, Middlesex, Radnor, Merioneth, Cheshire, Mid Lancs, Isle of Man, Renfrew, Peebles, Selkirk, Linlithgow, N. Aberdeen, Westerness, and in Clyde Isles, E. Ross, and E. Sutherland. It is rare in West of Scotland, and in Cornwall. It ascends to a height of 2000 ft.

The Rock Rose, while especially a plant of the chalk downs, is found elsewhere on hilly ground where a certain amount of lime occurs on more stony substrata. It is accompanied by Dog Violet (Viola ericetorum), Heath Milkwort (Polygala depressa), and other plants, such as Horse Shoe Vetch, Anthyllis vulneraria, etc.

This little plant is trailing, shrubby, with many prostrate stems, smooth below, and hairy above, adapted to growing on and amongst rocks. The leaves are linear-oblong, or acute, shortly stalked, with rolled-back margins, and deep-green, above rough to the touch, hoary below, and with 4 hairy lance-shaped stipules or leaflike organs. Some species of Rock Rose have no stipules, having broad-based leaves which serve to protect the buds. In H. guttatum the upper leaves bear stipules, and are narrow at the base, whilst the lower bear no stipules and have broad bases.

The flowers are large, golden-yellow, opening in the sunshine, in loose racemes, with bracts or leaflike organs. The sepals are smooth, the inner ones blunt, ending in a point, and three-nerved. The style is longer than the ovary, and bent at the base, equalling the stamens, which when touched will spring back and lie upon the petals. The stigma ends in a knob. The seeds are numerous, and the capsule, which opens by three valves, is enclosed by the longer calyx.

The plant is never more than 6 in. high and prostrate. The flowers last from May to September. The Rock Rose is a perennial, evergreen, trailing plant, increased by means of cuttings.

There is no honey but abundant pollen. The stamens are numerous (150). The pistil projects above them, and insects alighting on the flower touch the pistil before the stamens and cross-pollinate the plant with pollen from a previously visited flower. Self-pollination takes place if no insects visit it. There are 3 sepals and 5 petals which open in the sun. The anthers and capitate stigma mature together, the latter being a little taller. The anthers are at first close, but move outwards, and dust the insect which touches them with pollen, thus exhibiting irritability. The flower is best visited by the first insects from the corolla and by late-comers from the centre. The insect covered with pollen on a previous flower alights in the centre in the second and cross-pollinates it. Independently of insects' visits it is self-pollinated in closed and nodding flowers. There is abundant pollen sought by Diptera (Syr-phidae), Hymenoptera (Apidae), Coleoptera (Cerambycidae).

Rock Rose (Helianthemum Chamaecistus, Mill.)

Photo. Flatters & Garnett - Rock Rose (Helianthemum Chamaecistus, Mill.)

The Rock Rose disperses its seeds by the aid of the wind. The capsule splits into 3-5 valves, the seeds being jerked out and dispersed by the wind. The plant is a lime-loving plant requiring a lime soil, but where that desideratum is wanting it is a rock plant, growing on various rocky subsoils.

It is galled by Diplosis helianthemi. The beetles Bruchus ater, B. Cistii, and the Lepidoptera Hypochalcia ahenella, Butalis fuscoalnea, Teleia sequax feed upon it, also Brown Argus (Polyommatus artaxerxes), the dark Annulet (Coleophora ochrea), and Laverna miscella.

The name Helianthemum, given by Cordus, is from the Greek helios, sun, anthemos, flower, in allusion to its habit of opening its flower when the sun is out. Chamaecistus is from the Greek chamai, on the ground, and cistus, a shrub.

The English names are Rock Rose, Sot Flower, Sun Daisy, Sun Flower, Sun Rose.

This plant is often cultivated in gardens as a rock plant. Cuttings are easily made from it under glass. White and double flowers occasionally occur.

Essential Specific Characters:41. Helianthernum Chamaecistus, Mill. - Dwarf shrub, leaves oval, opposite, with fringed stipules, green above, hoary below, flowers yellow, in a raceme, with bracts, style bent below, sepals 5, 2 small, blunt.