| Aspidostemon | |
|---|---|
| Scientific classification | |
| Kingdom: | Plantae |
| Subkingdom: | Tracheobionta |
| Division: | Magnoliophyta |
| Class: | Magnoliopsida |
| Subclass: | Magnoliidae |
| Order: | Laurales |
| Family: | Lauraceae |
| Genus: | Aspidostemon Rohwer & H.G.Richt. |
| Especies | |
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See text |
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| Synonyms | |
Aspidostemon is a botanical genus of flowering plants belonging to the family Lauraceae. It is present from Madagascar.[1]
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The genus was described by Gunter Jens Rohwer & HGRicht. Published in Jahrbuch für Botanische Systematik, Pflanzengeschichte Pflanzengeographie und 109 (1): 74 in 1987. The type species is Aspidostemon perrieri (Danguy) Rohwer. They are known mostly from collections made during the last 20 years by staff of the Missouri Botanical Garden and their collaborators. A small number of collections were studied by Rohwer and Richter. Overall, the number of collections available is not large.[2] The identification was done at the Missouri Botanical Garden.
In a recent generic classification of Lauraceae based on DNA sequence data by Chanderbali et al. in 2001, was found to be part of a strongly supported clade that also includes Beilschmiedia, Potameia, Endiandra and Cryptocarya.[2] Because of the special lack of worldwide knowledge about the family lauraceae in general, very little is known about their diversity. The knowledge of this family to national level, is that to be expected in countries with limited economic means with the vast majority of species indeterminate or even poorly determined. On the other hand, a high percentage of recently described new species come from collections made in these countries. Therefore an increase in the study of family, at national level, is of utmost importance for the progress of the systematics of the family in general. Recent monographs of genera of lauraceae in small and medium genus, up to 100 species, have produced a high increase in the number of known species. This high increase in the number of species is expected for other genus, particularly for those with more than 150 species recorded, bringing an expected considerable increase in the total number of species of the family.
They are shrubs or trees up to 25 m high, hermaphrodites. The leaves are entire, elliptical or narrowly elliptical. The fruit is a berry dispersed mostly by birds. Aspidostemon species are no exception among the Lauraceae; trees with small flowers, hard to detect and collect and often overlooked or ignored when plants easier to collect or with showier flowers are at hand.
Aspidostemon, endemic to Madagascar, is a genus characterized by its opposite leaves, flowers with three or six two-locular stamens and a fruit which is completely enclosed in the enlarged hypanthium with persistent floral parts attached to the top of the fruit. The genus was described by Rohwer & Richter in 1987; they recognized 11 species, but today 28 species are accepted, one species is transferred from Cryptocarya to Aspidostemon, one is excluded from Aspidostemon and one is listed as incompletely known because the type specimen is sterile. Some species are endangered or almost extinct.[2] Based on a combination of wood anatomical, vegetative and floral characters, noted by such earlier botanists as Kostermans in 1957, the species of genus Aspidostemon were placed formerly as belonging to subgenera Hexanthera and Trianthera of Cryptocarya.[2]
Aspidostemon have the large trees characteristics of Rainforest in montane laurel forest habitats in Madagascar and nearest islands and restricted to this region. They belong to an ancient isolated Gondwanian element of Laurales. A great number of species are in danger of extinction due to over exploitation as timber extraction and also for loss of habitat.
They are leafy canopy trees with erect or spreading branches. It grows to heights of up to 25 metres some species 40 m. and have stout trunks up to 1 metre in diameter. Aspidostemon is easily recognizable by its bark which is soft and cheese-like. The thick, leathery leaves are dark green. The leaves are glossy laurel type. The leaves of Aspidostemon species are not infrequently acuminate, with an acumen that is folded into a short tube, not flat. On opening a few of these inrolled apices, it is noticed egg-cases similar to those found in leaf domatia; epiphyllous hepatics were also found. It seems that these inrolled apices function as domatia and shelter mites that clean the leaves.
The forests are made up of laurel-leaved evergreen hardwood trees, harbouring a rich biota of understorey plants, invertebrates, reptiles, birds and mammals. The species of Aspidostemon genus require continuously moist soil, and do not tolerate drought.
Trees or shrubs, monoicous. The ecological requirements of the genus, are those of the laurel forest and like most of their counterparts laurifolia in the world, they are vigorous species with a great ability to populate the habitat that is conducive. Aspidostemon genus respond to characteristic formations of laurel forest. The natural habitat is rainforest which are cloud-covered for much of the year. These species are found in forests that face threats of destruction by human deforestation. It could caused the extinction of the genus across the restricted region area, resulting in the present distribution. Some species are in danger of extinction due to loss of habitat. Aspidostemon is a genus of great ecological importance. It is present in coastal low rainforest and montane rainforest, laurel forest, in the Weed-tree forests in valleys, mixed forests of coniferous and deciduous broad-leaved trees. Originally from Madagascar. The differences are ecological adaptations to different environments over a relatively dry-wet climate. Species in less humid environment are smaller or less robust, with less abundant and thinner foliage and have oleifera cells that give trees a more fragrant aroma. The most known trees are used by the timber industry. In this genus the wood of some species are having a high commercial value.
The species forming this genus share a unique paniculate inflorescence with the ultimate divisions that are not quite cymose; that is, the lateral flowers of what looks like a cyme are not strictly opposite, but tend to be subopposite, while in most genera of Lauraceae with paniculate inflorescences the lateral flowers in a cyme are strictly opposite. Most species of Aspidostemon have small, few-flowered inflorescences, but in a few species, such as A. glandulosum, inflorescences are sufficiently large and branched that one can observe the inflorescence type is that found in the Beilschmiedia. Aspidostemon is related to the Beilschmiedia clade and that, based on the presence of fruit included in the enlarged hypanthium, it is yet most closely related to Cryptocarya thought the similarity in fruit structure, in both Aspidostemon and Cryptocarya the fruit is enclosed in the enlarged hypanthium, might be a parallel development and not a signal of common ancestry. The fruit, a berry, is an important food source for birds, usually this birds are from specialized genus. Birds eat the whole fruit and regurgitate seeds intact, expanding the seeds in the best conditions for germination (ornitochory). In some species the seed dispersal is carried out by mammals.