Hoya rigidifolia
| Hoya rigidifolia | ||||||||||||
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Inflorescence, leaves and pollinarium |
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| Scientific name | ||||||||||||
| Hoya rigidifolia | ||||||||||||
| S.Rahayu & Rodda |
Hoya rigidifolia is a plant of the genus of wax flowers ( Hoya ) of the subfamily of asclepiadoideae (Asclepiadoideae).
features
Hoya rigidifolia is an epiphytic , climbing plant. The shoots have a diameter of 3 to 54 mm and are freshly dark brown and sparsely hairy, then gray and bare with age. Adhesive roots are formed below the nodes and along the internodes, with which the plant attaches to the ground (trunks and branches of trees). The internodes are 4 to 10 cm long. The opposite leaves are stalked, the petioles are 7 to 25 mm long and 4 to 6 mm in diameter. They are thicker than the shoots and light brown. The stems are round in cross-section and when freshly developed sparsely hairy, later glabrous. The stiff and succulent leaf blades are lanceolate to oblong, 4 to 12 cm (rarely up to 15 cm) long, and 2.5 to 5 cm wide. The base is pointed, the apex pointed and lobed. They are green to light green with a few gray spots on the top. The leaf nerve consists of the midrib from which two main veins branch off near the base of the blade, which run almost parallel to the edge. From the midrib and the secondary veins, 3 to 10 smaller veins lead off, which connect the midrib and secondary veins. The leaf veins are sunk on the top, the bottom is flat. At the base of the leaves there is a triangular, light brown to cream-colored gland, approx. 1 × 1.5 mm. All vegetative parts of the plant excrete a white milky sap when injured.
The umbel-shaped inflorescences arise from the leaf axils and are horizontal, only one inflorescence is formed per leaf axil. The inflorescences each contain about 20 to 25 flowers. They have a kovex curved surface with a diameter of 3.5 to 4 cm. The brownish, sparsely hairy inflorescence stalks are 1.5 to 3 cm long and measure approx. 3 mm in cross section. The finely papillary pedicels are 13 to 17 mm long, 0.7 to 1 mm thick and light brownish yellow. The sepals are ovate or rounded and 1 to 1.5 mm long and 0.8 to 1 mm wide at the base. The apex is rounded, the outside finely papillary. The corolla is wheel-shaped and, when spread out, is 10 to 12 mm in diameter. The bald petals are ovate, 3.3 to 3.7 mm and at the base 2.4 to 2.8 mm wide. The pointed apex is strongly bent. They are cream-colored on the inside and light brown towards the tip, brown on the outside. The white secondary crown is 1.2 to 1.4 mm high and measures 3.7 to 4.2 mm in diameter. The egg-shaped tips are 2 to 2.3 long and 1.1 to 1.2 mm wide, lie on the back of the stamens and are at an angle of about 80º. They form an angle at the top. The inner extension is pointed, the outer extension is rounded. The stamens are egg-shaped, approx. 0.7 × 0.6 mm and have a thin, round appendix at the apex. The flowers of Hoya rigidifolia are only open one day before they die.
In the pollinarium , the pollinia are 350 to 400 μm and 130 to 150 μm wide. They are elongated with a rounded base and a truncated, inwardly sloping apex. They have a transparent outer edge. The caudiculae are very short, approx. 40 × 20 μm. The elongated corpusculum is 120 to 140 μm and approx. 50 μm wide. The stylus head is pentagonal in cross-section with five lobes that alternate with the stamens. The apex is roughly sunk with a central point, about 200 μm high. Fruits and seeds have not yet been observed.
Similar species
The flowers of Hoya finlaysonii are also only open one day before they perish and have a very similar flower structure (wheel-shaped corolla, egg-shaped corolla of similar size). The two types differ in the leaves. Hoya finlaysonii has lanceolate to elongated leaves and pinnate leaf veins that are usually darker than the leaf itself. Hoya rigidifolia also has a pinnate leaf nerve, but has two secondary ribs, which branch off from the midrib near the base and then extend almost parallel to the edge over the entire leaf.
The leaf nerve of Hoya erythrina Rintz (1978) is very similar to Hoya rigidifolia , but the flowers are very different. The flowers of Hoya erythrina have a diameter of> 15 mm ( compared to <12 mm in Hoya rigidifolia ) when they are spread out. They are hairy long and downy on the inside. They stay open for more than 2 days, while the flowers of Hoya rigiflora already fade after one day.
Geographical distribution and habitat
Hoya rigidifolia is so far only of the type locality in a lowland rainforest about 100 m above sea level, near Pulau Siberut, Mentawai Islands , West Sumatra , Indonesia.
Taxonomy
The taxon was established in 2019 by Sri Rahayu and Michele Rodda. The holotype has been deposited in the herbarium of the Research Center for Biology in Cibinong, Indonesia under the number S. Hidayat B9710110. The new species was named after the relatively stiff leaves.
literature
- Sri Rahayu, Michele Rodda: Hoya of Sumatra, an updated checklist, three new species, and a new subspecies. In: European Journal of Taxonomy. No. 508, 2019, pp. 1–23 ISSN 2118-9773 doi : 10.5852 / ejt.2019.508