The Liliales (lilies) is a large order of plants containing some 8,000 different species in the world, in a dozen or more families. These are widely distributed but are particularly a feature of the temperate and subtropical regions.
Adaptations to environments
Characteristically the plants are perennial terrestrial, but there are a few . A number of species in warmer climates are large, woody and treelike in their growth. There are a few climbers and one family, the Ponte-deriaceae, are aquatic that include the notorious cosmopolitan weed water , Eichhornia crassipes, which bears colourful spikes of above the rafts of floating .
A striking feature of the group is their variety of adaptations to survive inhospitable climates or seasons. Several families have evolved bulbs, corms or tubers as underground food stores which enable the plants to survive unfavourable conditions. For example the colourful bulbous and tuberous plants such as tulips, crocuses, irises, fritillaries, garlics and grapeare all characteristic plants of the hot arid Mediterranean garigue. These plants largely contribute to the colourful spectacle of this landscape in the spring, which quickly gives way to scorched stony hillsides during the summer months.
The agaves of America and aloes of Africa are able to survive in dry desert climates by means of their tough succulent leaves andwhich store water and are resistant to water loss.
Flower structure in the order is usually fairly uniform with a corolla composed of six perianth segments. The three outer segments are the sepals while the three inner segments are the petals, but normally they are closely similar in shape and colour. Themay be large, showy and solitary as in the tulips, Tulipa sp., or they may be borne in long racemes of small flowers as in the Mediterranean plant sea squill, Urginea maritima. The latter is remarkable for its enormous bulbs which may be as much as 15cm (6in) across and may project out of the ground on dry stony hillsides. The flowers of the onion and garlics, Allium spp., are relatively small but may be clustered into large globose heads. The European wild crow garlic, Allium vineale, does not often produce normal flowers but has a small spherical head of tiny bulbs or bulbils which sprout young leaves before they are shed to grow into adult plants.
Lily flowers are usually pollinated by insects. The perianth segments normally form a tubular- shaped flower at the base of which nectar is produced. Visiting insects have to push past the stamens to reach the bottom of the tube. In the temperate genus Fritillaria the flower is a hanging bell formed from six free perianth segments which produce nectar in grooves at their bases. The stigma, which projects beyond the stamens, matures first so that the chances of cross-by visiting bumblebees are increased.
In the nodding star of Bethlehem, Ornitho-galum nutans, the filaments of the stamens form a tube while the perianth segments are spreading for.
Several members of the order have unusual pollination mechanisms. In the American yuccas of the family Agavaceae there is a remarkable relationship between the flowers and their pollinator, a small tineid moth. The creamy-white flowers of theare produced in showy inflorescences and are sweetly scented at night to attract the moths. The female moth visits the flowers descending into one and climbing the stamens one by one to collect pollen with her maxillary palps. The moth then flies to another flower where she inspects the ovary and if the flower is suitable she bores into the ovary to lay an egg. She then climbs up to the stigmas which form a tube and thrusts pollen into the tubular structure. Un-pollinated flowers die quickly but pollinated flowers develop to ripe fruit, part of which nourishes the larval moths. The plant therefore provides food and shelter for the moth which in return pollinates the flowers.
Use to man
A few members of the order produce useful or economically valuable products. The extraordinary treelike dragon tree,draco, which is a native of the Canary Islands, and another member of the same genus produce red resins known as dragon’s blood which are used in varnishes.
The meadow saffron, Colchicum autumnale, of Europe and North Africa yields an alkaloid drug colchicine which is extracted from the corms and is used medically for treating rheumatism and gout. The drug is better known for its controlling effect on chromosomes which has facilitated the study of this aspect of cell science.
Several members of the genus Allium are important as food crops or flavouring materials. The onion, A. cepa, which probably originated in Asia, has been an important and widely cultivated Allium. The bulbs are eaten raw or cooked, and are widely appreciated for their characteristic pungent flavour. Chives, A. schoenoprasum, widely distributed in the north temperate region, has tufts of longitudinal leaves and heads of pinkish purple flowers. The mild flavoured leaves are used principally for garnishing. The closely related leek, A. ampelo- prasum var. porrum, originated in the eastern Mediterranean and is cultivated as a vegetable.
A number of yams of the genus Dioscorea are of local economic importance in the tropics. These predominantly tropical herbaceous climbers such as D. alata produce edible starchy tubers which are a staple food in parts of West Africa.
Several species of agave, natives of the arid and semiarid tropics of Central America, especially Mexico, are cultivated or harvested for their fibres. These perennial plants produce massive flower spikes from basal rosettes of stiff spiky leaves which yield long hard fibres. Sisal, A. sisalana, produces coarse fibres which are particularly useful in the manufacture of twines and cordage, while the chopped fibres may be used as a re-inforcing material for plaster-boards.
The related century plant A. americana is often planted for its decorative foliage. The majority of garden plants belonging to the lilies are small herbs that are grown for their colourful and decorative flowers. These include all the spring bulbs and related flowers that are such a feature of gardens in north temperate countries. Very early flowering species such as the, nivalis, come into flower during the winter months. These are followed in early spring by the first flush of colour provided by a variety of cultivated crocuses which originate from southern Europe. The daffodils and narcissi, belonging to the temperate genus , also flower at about the same time. Tulips, which are late spring bulbs, were introduced from western Asia to Holland and other west European countries in the sixteenth century, where they have been cultivated ever since. Tulips are grown commercially for their flowers in Holland, the Fenlands of eastern England and in America. A variety of true lilies, genus Lilium, which are cultivated as garden flowers, originated in temperate Asia, especially China, and Japan, and also in America. The late flowering bulbs of European gardens are mainly South African in origin such as the spectacular blue flowered Agapanthus africana and the rose pink nerines.