This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
As with Furze, commonly distributed as it is this shrub is not found in any early deposits. Its present range is from Gothland southward, but it is absent from Greece and Turkey, occurring in N. Asia, Canaries, and the Azores. In Great Britain it is found in every county except Cardigan, Flint, and the Northern Isles, from Caithness southward, up to a height of 1000 ft. in the Highlands. It is found in Ireland and the Channel Islands.
Broom is everywhere a sign of heath-land or common-land, equally as much as Furze; but to-day Broom bears much more evidence of having been planted than Furze does, being much employed for forming fox-coverts and plantations, where Furze is used in its natural state. Railway embankments are frequently lined with clumps of Broom, and it grows in many recent woods.
Broom is a typical switch plant, with the shrub habit. The plant is more or less hairy, but not spinose, as in Furze, to the habit of which it more or less conforms, both being dry-soil heath plants. The stems are erect, much branched, bright- or dark-green, angular, and furrowed, the branches silky. The leaves are shortly stalked, ternate, 3 in a group, or solitary. They are small or absent, and the stems perform their function to a great extent. The leaflets are inversely egg-shaped, silky.
The flowers are papilionaceous, large, bright-yellow or white, the flower-stalks short, in the axils, solitary or paired. The styles are spiral. The pod is black, with hairs along the borders, and many seeds. After opening, the valves are twisted.
The height of a Broom plant is about 6 ft. It is in flower in April, May, and June. The plant is an evergreen shrub, increasing by seed.
The flowers are, as in Genista, explosive. There is no honey. The 5 short stamens first explode and dust the insect's abdomen, the 5 longer stamens then dust it above, and the pollination of the stigmas not covered up ensues. When bees settle they grasp the alae with their mid and hind legs, and thrust their forelegs and head below the middle of the vexillum or standard.
The alae and carina are forcibly pressed down, and the united upper margin of the keel splits from behind forwards by the pressure of an insect's foot. A fold catching in the angle between the upper edge of the carina and the sharp pouched protuberance at its mouth connects the alae with the carina. When the split extends to the middle the shorter stamens spring out. They open in the bud and now press the pollen against the closed upper edge of the carina, and force the pollen against the bee's abdomen. The shock is not sufficient to drive off the bee, which only pauses and resumes its work. The split extends still further, and has barely reached the tip of the style, closely pressed against the keel, when a second more violent explosion takes place. Before this the style lay along the side of the carina, and the flattened end lies in the apex of the carina above the longer anthers, which have already opened. It curls inwards being now rendered free, and forms more than one complete spiral turn. As soon as it extends to the end of the carina the style springs up, and strikes the bee's back with the stigmatic tip, and the bulk of the pollen carried away by the enlarged style falls on the bee's back. The long stamens curl inward and emerge from the flower. When the bee is held, and the stigma cannot slip sideways, it remains as if stunned, and then, turning round, forces itself away from the style, and begins to gather pollen from the anthers. When the vexillum is erect, and the alae are still enclosed by it, humble bees force it open and cross-fertilize it. The visitors are Hymenoptera (Apidae), Diptera (Syrphidae), Coleoptera (Staphylinidae, Nitidulidae).
Broom is dispersed by its own agency. The fruit is a dry pod. which jerks its seeds by an elastic movement, to a distance, opening suddenly with a jerk. It is also myrmecochorous, or dispersed by ants, which find nutriment in the elaiosomes.
Broom is a heath plant requiring a sand soil, and is thus a sand-lover, but some degree of humus soil is also a necessity, and it is likewise partly a humus-lover.
It is galled by Asphondylia sarothamni. Other insects infesting it are Placophthorus rhododactylus, a beetle, and also the beetles Sitones regens, Philorhinium sordidum, Exochomus quadripustulatus, Meli-gethes lumbaris, Loemophloeus ater, Micrambe vini, Dryophilus anobi-oides, Bruchus villosus, Phytodecta olivacea, Luperus nigro-fasciatus; the moths, etc, Long-tailed Blue Butterfly (Polyommatus boeticus), Pale-shouldered Brocade (Mamestra thalassina), Straw Belle (Aspilates gilvarid). The Streak (Chesias spartiata), Depressaria assimilella; the Homoptera, Gargara genistae Psylla spartii; the Heteroptera, Piezo-dorus lituratus, Dictyonota strichnocera, Anthocoris sarothamni, Ortho-tylns adenocarbi, O. concolor, O. chloroptertts, Heterocordylus genista, H. tibialis, Ascodema obsoletum, and Megachile versicolor, a Hymenop-terous insect.
Photo. H Irving - Broom (Cytisus scoparius, Link.)
Cytisus, Pliny, is an old Greek name for a kind of clover. Scoparius is from the Latin scopoe, a broom.
Broom has been named Banadle, Bannal, Basam, Beesom, Bisom, Bizzom, Breeam, Greem Broom, Green Broom, Browme, Brum, Genest. Basam, Bassam, or Bisom were names given in reference to the habit of making brooms from it. Breeam tea was an infusion used as a diuretic.
If Broom has many flowers it is a sign of plenty. In Germany it is used in decorating at Whitsuntide. When Joseph and Mary were fleeing into Egypt it bristled and cracked.
"If you sweep the house with blossomed Broom in May, You are sure to sweep the head of the house away."
The water from Broom flowers was drunk by Henry VIII to prevent disease from surfeits. The bark shaved was used to stanch blood in the fourteenth century. An unguent was made from the blossoms. It was the badge of the Plantagenets.
The tops of Broom were put in beer to give it a bitter taste. The stem is fibrous, like Spanish Broom. The seeds have been used to adulterate coffee. Containing much alkali, it is the Sal genistoe of the pharmacopeia. It has been used successfully for thatching, and is planted for fences and coverts. It serves also as food for cattle. The flowers in bud are pickled like capers. The woody part was once used for tanning leather, and the old wood for veneering. Cloth has been manufactured with the fibre. It is cathartic, and the seeds emetic.
Essential Specific Characters: 75. Cytisus scoparius, Link. - Shrub, branches slender, erect, angular, leaflets small, scattered, ternate, upper simple, flowers yellow, large, pods hairy, black, styles coiled.