Microloma
| Microloma | ||||||||||||
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Microloma calycinum , Richtersveld National Park , Namakwa District , Northern Cape , South Africa |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Microloma | ||||||||||||
| R.Br. |
Microloma is a genus of plants in the subfamily of the silk plant family (Asclepiadoideae) within the family of dog poison plants (Apocynaceae). There are about twelve species in the Microloma genus, all of which are native to South Africa and southern Namibia .
description
Vegetative characteristics
The Microloma species are woody creepers or shrubs that grow up to around 100 cm (or 150 cm) tall. The milky juice is colorless. The woody rhizome consists of fibrous, spindle-shaped or bulbous roots. The plants are long-lived, the main stem axis reaches a diameter of 5 cm at the base. Usually only a single, woody shoot appears on the surface, which then branches off at a certain height above the ground. The shoot axes have a cork-like bark , which is also thickly felty in some places. The plant hair lies close to the surface. In some species, the above-ground parts of the plant die off during the summer drought, in other species, apart from the very young shoot axes, no death during the summer drought can be observed.
The leaves are persistent or also decrepit. They are mostly opposite or rarely alternating and sit almost directly on the stem axis. The leaf blades are fleshy or leathery, 0.4 to 7 cm long, 0.1 to 0.7 cm wide with a triangular, elliptical or linear shape, basal also wedge-shaped or ear-shaped. They are bald, sparsely hairy to densely hairy.
Inflorescence and flowers
The numerous individual inflorescences do not arise from the leaf axes, but alongside the leaves. They are subsessile to stalked, shorter than the leaves and 1 to 15 flowers. The inflorescence shafts are about as long as the flower stalks, little and finely hairy. The flower stalks are also hairless or finely hairy. The flowers of an inflorescence develop almost simultaneously in most species. The inflorescences often bloom at the same time. However, other species form flowers over a longer period of time (for example Microloma sagittatum and Microloma calycinum ).
The calyx is about half the length of the corolla. The calyx is bell-shaped or twisted and fused at the base. The sepals are lanceolate to triangular and apically pointed. They usually have the same color as the lower part of the corolla, more rarely green. Exceptions are Microloma calycinum and Microloma penicillatum , whose long, lanceolate sepals are spread out and are pink-red or deep red in color. The corolla is 2 to 9 mm long, cylindrical, rather tubular or widening slightly towards the base (urn-shaped), often also a little constricted in the middle or a little swollen around the mouth. It is more or less clearly rounded on five sides in cross section. The petals are usually fused between half and 3 quarters of the total length (or over the entire length) and provided with longitudinal ribs (= strongly convex outwardly curved petals). They are white, yellow, orange-red or red at the base and greenish to yellowish at the top. They are seldom glabrous or finely fluffy inside, usually very hairy or. If the inside is hairy, then the downward, stiff hairs are concentrated in a ring around the apical part of the gynostegium . The tips of the petal lobes are turned slightly to the right. The petals are rounded triangular or broadly rounded to almost rounded, curved inward, and the corolla tube is thereby closed. A staminal side crown is missing. The gynostegium is stalked and almost enclosed in the corolla. The apex is tapered. The stamens are triangular and apically bluntly tapered. They are significantly longer than they are wide and have a narrow channel on the outside, a kind of " guide rail ". The pollinia are 0.5 to 1 mm. The flowers produce plenty of sweet nectar, which can largely fill the inside of the corolla tube.
Fruits, seeds and germination
The smooth, light brown follicles stand solitary and hang. They are 2 to 10 cm long and 4 to 8 mm in diameter. A follicle fruit contains 3 to 35 seeds. The number of seeds per fruit is constant within certain limits within the species. The seeds are light brown to brown-yellow, occasionally pink, and pear-shaped in outline. The top is more or less flattened, the underside strongly arched.
Germination is greatly delayed: from sowing to germination it takes 3 to 8 days, even under favorable conditions.
Chromosome numbers
The number of chromosomes is 2n = 20 (in Microloma incanum , Microloma sagittatum and Microloma tenuifolium ).
ecology
The flowers of the Microloma species are practically closed for the duration of the anthesis . They prevent the penetration of small insects, for example ants, which would consume the abundant supply of nectar, but are not suitable for fertilizing the flower or are not able to fertilize the flower because the relatively large pollinia from one flower to the other are too small to transport others. The flowers can only be opened by large insects with a long proboscis. The stiff hair and the guide rails on the outside of the stamens largely prevent lateral movement of the trunk; the proboscis, with the elongated pollinia attached, is guided downwards through the downward-facing hairs on the inside of the corolla and the guide rail on the outside of the stamens. Pollinia brought along are stripped off at the lower end of the guide rail when the trunk is withdrawn and new pollinia may be torn off and stick to the trunk.
Occurrence
The Microloma species occur in the Republic of South Africa and in Namibia in the area of winter rain. In the Republic of South Africa these are the provinces of the Western Cape , Northern Cape and Eastern Cape . In the mountains they rise to altitudes of 2000 meters. So there are floral elements of the Capensis .
Systematics
The genus was established by Robert Brown . The type species is Microloma sagittatum (L.) R.Br.
There are currently around 12-13 species in the Microloma genus :
- Microloma armatum (Thunb.) Schltr. ex Gilg (with the two varieties Microloma armatum var. armatum (Syn .: Microloma massonii (Schult.) Schltr. ) and Microloma armatum var. burchellii (NEBr.) Bruyns ): It occurs in southern Africa.
- Microloma calycinum E. Meyer : It occurs from southwestern Namibia to the northern Cape Province.
- Microloma hereroense Wanntorp : It occurs in western Namibia.
- Microloma incanum Decne. : It occurs from Namibia to the northern Cape Province.
- Microloma lanatum Wanntorp : It occurs in Namibia.
- Microloma longituba Schltr. : It occurs from Namibia to the northern Cape Province.
- Microloma namaquense H. Bolus : It occurs in the north-western Cape Province.
- Microloma penicillatum Schltr. : It occurs in southwestern Namibia.
- Microloma poicilanthum H.Huber : It occurs from southwestern Namibia to the northern Cape Province.
- Microloma sagittatum (L.) R.Br. (Syn .: Microloma hastatum Decne. ): It occurs only in the Cape Province.
- Microloma tenuifolium (L.) K.Schum. (Syn .: Microloma lineare R.Br. ): It occurs in the southwestern Cape Province.
No longer counted in this genus:
- Microloma angustifolium Buch.-Ham. ex Hook.f. => Leptadenia pyrotechnica (Forssk.) Decne.
supporting documents
Individual evidence
- ↑ a b c d Bruyns & Linder (1991: 453ff.)
- ^ Henning Kunze: Structure and function in asclepiad pollination. Plant Systematics and Evolution, 176: 227-253, 1991 doi : 10.1007 / BF00937909
- ↑ a b c d e f g h i j k l Rafaël Govaerts (Ed.): Microloma - World Checklist of Selected Plant Families des Royal Botanic Gardens, Kew. Last accessed on November 7, 2018.
literature
- Peter Vincent Bruyns and Hans Peter Lindner: A revision of Microloma R. Br. (Asclepiadaceae - Asclepiadeae). In: Botanical Yearbooks for Systematics, Plant History and Plant Geography , 112, Stuttgart 1991, pp. 453-527.
