Annual species complete their life cycle during favourable seasons and pass unfavourable ones as seeds. Bulbous plants, on the other hand, have developed storage organs as a reserve to allow them to survive unfavourable conditions in a resting condition in order to begin growth again when environmental conditions become more favourable. The dormant or resting period may be in summer or winter, or may depend on rainfall, as in the tropics. The different strategies enable bulbous plants to survive adverse conditions such as extremely hot and dry summers, very cold winters, or periods of drought.
Summer dormancy '' flowering on 15 November in Greece Most bulbous plants are adapted to hot, dry summers and cooler, wetter winters. They are dormant through the summer and grow during the autumn, winter and spring. Within this group, there are variations, largely determined by how cold the winter is. Many
tulips (
Tulipa species) of Asian origins, for example, have adapted to an extreme continental climate, with dry, very hot summers, very cold winters and springs with short showers. They grow mainly during the spring. In cultivation such tulips may be planted in late autumn (e.g. November in the northern hemisphere). In regions where winters are milder, some species, such as
Crocus cartwrightianus, flower in the autumn, either at the same time as the leaves appear or before. Others, such as
Arum creticum, produce leaves in the autumn which last through the winter until the plant flowers in the spring. Summer drought occurs particularly, but not exclusively, in those regions of the world with a
Mediterranean climate, which are rich in bulbous plants. Such regions include the
Mediterranean itself through to
Central Asia, the south west of South Africa, the south west of Australia, parts of the western United States, such as
California, and parts of western South America, particularly Chile. in
Kent, England Many species that grow in the
understory of deciduous woods or forests are also summer dormant. They use their stored reserves in order to grow rapidly and complete their annual growth-cycle at the beginning of spring before the developing tree canopy blocks out the sun's light. North America is home to many such woodland bulbs, including
Erythronium,
Trillium and some lilies, such as
Lilium pardalinum. The common bluebell,
Hyacinthoides non-scripta, is native to western parts of Europe, but particularly the British Isles, where it carpets the floor of some woods. The woodlands of Asia, including China and Japan, are home to bulbous plants such as
arisaemas and the giant
cardiocrinums. Some bulbous plants grow in
communities that are adapted to recurrent fires during the dry season (for example, many
Iridaceae species). During these periods the plants are dormant and in this way can survive the heat of the fire. The fires clean the surface vegetation, eliminating competition and also supplying nutrients to the ground from the ashes of the burnt plants. When the first rains fall, the bulbs, corms and rhizomes rapidly start to shoot, starting a new period of growth and development sustained by the reserves accumulated in their storage tissues during the previous season. Various South African species from the genus
Cyrtanthus, for example, are well known for their ability to flower rapidly after natural grassland wildfires, and for this reason several of these species are known as "fire lilies". In fact, some species, such as
Cyrtanthus contractus, only flower after a wildfire.
Winter dormancy '', a winter dormant bulbous plant A second category of bulbous plants are those adapted to dry, generally cool winters and warmer, wetter summers. They are dormant through the winter and grow in spring, summer and autumn. Regions of South Africa and Lesotho with this type of climate include the East Cape, and the
Drakensberg mountains in the north east of
Western Cape province, which are particularly rich in bulbous species, including plants such as
gladioli,
Eucomis and
Rhodohypoxis. Other areas with similar winter drought include parts of Central America, such as Mexico where the tiger flower (
Tigridia pavonia) is found.
Seasonal dormancy In some areas of the tropics, rainfall is interspersed with periods of dryness; more than one wet/dry cycle may occur in a year. Bulbous plants in these areas are adapted to warm, wet periods followed by warm, dry periods. They typically flower near the beginning of the rainy season. Such a climate occurs in Kenya, which has wet conditions in October to December and then again in February to May. Glory-lilies (
Gloriosa) and
Crinum species are examples of bulbous plants adapted to these conditions. Tropical Asia has similarly adapted bulbous plants, such as species of
Hedychium (gingers). == History of use ==