Sundews are perennial (or rarely annual) herbaceous plants, forming prostrate or upright rosettes between 1 centimeter (0.4 in) and 1 meter (39 in) in height, depending on the species. Climbing species form scrambling stems which can reach much longer lengths, up to 3 meters (10 ft) in the case of D. erythrogyne. Sundews have been shown to be able to achieve a lifespan of 50 years. The genus is so specialized for nutrient uptake through its carnivorous behavior that the pygmy sundew is missing the enzymes (nitrate reductase in particular) that plants usually use for the uptake of earth-bound nitrates.
The genus can be divided into several growth forms:
• Temperate Sundews: These species form a tight cluster of unfurled leaves called a hibernaculum in a winter dormancy period (= Hemicryptophyte). All of the North American and European species belong to this group. Drosera arcturi from the mountains of New Zealand is another temperate species that dies back to thick, wiry roots.
• Subtropical Sundews: These species maintain vegetative growth year-round under uniform or nearly uniform climatic conditions.
• Pygmy Sundews: A group of roughly 40 Australian species, they are distinguished by miniature growth, the formation of gemmae for asexual reproduction, and dense formation of hairs in the crown center. These hairs serve to protect the plants from Australia's intense summer sun. Pygmy sundews form the subgenus Bryastrum.
• Tuberous Sundews: Nearly 50 Australian species that form an underground tuber in order to survive the extremely dry summers of their habitat, re-emerging in the autumn. These so-called tuberous sundews can be further divided into two groups, those that form rosettes and those that form climbing or scrambling stems. Tuberous sundews comprise the subgenus Ergaleium.
• Petiolaris Complex: A group of tropical Australian species which live in constantly warm but irregularly wet conditions. Several of the 14 species that comprise this group have developed special strategies to cope with the alternately drier conditions. Many species, for example, have petioles densely covered in trichomes, which maintain a sufficiently humid environment and serve as an increased condensation surface for morning dew. The petiolaris complex comprises the subgenus Lasiocephala.
Although they do not form a single strictly defined growth form, a number of species are often put together in a further group:
• Queensland Sundews: A small group of three species (D. adelae, D. schizandra and D. prolifera), all native to highly humid habitats in the dim understories of the Australian rainforest.
Source: http://en.wikipedia.org/wiki/Drosera
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