This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Man during his operations in one direction or another, by agriculture, horticulture, building operations, quarrying, railway or canal transit, causes considerable disturbance in the balance of nature by the introduction, unconsciously (as a rule), of many plants which are called aliens, casuals, colonists, denizens, etc. Collectively considered there are some 1100 aliens which come to us with seed from abroad, in cotton, etc, and are often to be found straying from mills where wheat is ground for flour, the small seeds being blown away in the winnowings.
A few are called Viaticals, and may be found along our waysides, having travelled thus by various means, there being seventy of these. The former use of herbs in medicine is responsible for a number of these.
Moreover, the carrying of corn with its complement of weeds along our highways, a necessary operation, causes the agrestal type of plants to find a place also along our highways and in those other places which are especially visited by man. Of these Mesophytes (treated in Section III) there are about 110, and a number of them are common to waste ground, as this last is often associated with the place of storage of cultivated plants.
The distribution of this class of plants being entirely artificial, it should naturally come at the end of the series, followed by the equally artificially-placed mural plants which are allied to the natural Litho-phytes. These aliens cannot be regarded as identical with that group called Chersophytes, or waste herbage which grows on land formed by the cutting down of forests often removed from human habitations and on high land. At the same time it is allied to it, growing on dry soil, which is the usual characteristic of the soil of the waste places here referred to. Such soil is usually dry, sandy, often loose, or in the case of farmyards moist and rich in nitrogen. These weeds are hardy, often woody-stemmed plants which oust the native plants. They are usually annual, often biennial, and while some are ephemeral and remain a year only, others become well-established for several decades, such as Mallows. Most of them are xerophilous and have hairy stems. A few are shade-dwellers, but the bulk live in the open and are sun-lovers. They are all hardy strugglers, and not only herbaceous plants, but even shrubs, are liable to be choked by an alien incursion of weeds.
An Act to prevent the introduction of alien weeds into Ireland has been passed, and it is desirable that this be extended to England and Wales.
Waste places as a whole are diverse in origin and character. We have selected a few of the types, and include about thirty-three species.
We have first of all hedgerow plants, which owe their introduction largely to a former use in herbal medicine, such as Greater Celandine, which grows under the hedge bounding a cottage garden close to a village. Here also, and always close to a building, one finds Gout-weed, once used for gout, etc. Tansy is also found in the same sort of place. Strayed from the kitchen garden, again, we find Borage sheltered amongst the protecting branches of a low-trimmed hawthorn. The Bitter-sweet, usually found in the hedgerow, comes up luxuriantly in allotments, though it is also perhaps native in the marsh formation.
At the base of walls, where there is sand, one finds Common Mouse-ear (along with Chickweed, Sandwort, etc.) and Barley Grass, the last ubiquitous on waste sandy ground, with Barren Brome Grass, Rye, and Couch Grass. On sandy wastes, especially on dunes and roadsides, one finds Stork's Bill, and on hilly ground, Musk Thistle. Along a cart-road Viper's Bugloss may be found on chalky soils. Railway embankments are a fertile source of weeds, but we only enumerate two very common ones, Common and Creeping Toad Flax, which along the embankments near Reading hybridize.
One of the most profitable pieces of ground to draw for cultivated weeds is a farmyard or a stackyard, and around the margins of either it is easy to find amongst others the following: Shepherd's Purse, ubiquitous and in flower all the year (in autumn with purplish flowers coloured by anthocyanin), Common Mallow, forming large and tall handsome, woody, shrub-like clumps, with clusters of striking purple blooms. Here, too, we find tall, sweet-scented Melilot, the stinking May-weed, Burdock, Spear Thistle (which grows in fields too), the lovely blue-flowered Chicory, Hawksbeard (common everywhere in fields, &c), and Dairy-maid's Dock. Around gateways many common plants, as Great Plantain, Swine's Cress, Knotgrass, are predominant. In quarries or allotments the Deadly Nightshade is occasionally found. Gardens shelter many weeds, such as Wormwood, Groundsel, Mullein, Red Dead Nettle and White Dead Nettle (the latter also on roads), Good King Henry, and Fat-hen; and on kitchen-middens, Hound's Tongue and Henbane.