Hoya.
Family Apocynaceae > Subfamily Asclepiadoideae > Tribe Marsdenieae.
There are around 250 (200 – 300) species of Wax plants with 6 native to Australia.
They are evergreen, perennial, often succulent, mostly woody vines.
They climb by stem twining and sometimes by adventitious roots.
Most are epiphytes but some grow on the ground.
Some are creepers, a few are shrubby and some have a milky sap.
The opposite leaves, commonly thick and succulent, are on petioles.
The round, ovate, elliptic or almost linear blade is from 5 mm to 20 or 30 cm long.
Mostly a glossy, dark green to grey-green and some have a pale mottling.
One species H. pottsii, has dark purple leaves when in bright sun.
The leaf surface can be smooth or finely to densely hairy and some have glandular hairs.
The veins may be obvious or inconspicuous.
Inflorescences are occasionally a single flower but commonly umbels up to 30 cm across.
The peduncle, attached between the leaf bases, is known as a spur.
Unusually the spur remains attached and bears new clusters of flowers each season.
With each flowering the length of the spur increases reaching over 20 cm in some species.
The typically fleshy or waxy appearing flowers are from 3 mm to 10 cm or more across.
The star-like flowers, with parts in 5’s, are often scented.
The petals are commonly white to pink and the central star shades of red.
Other colours include cream, greenish, orange or yellow.
Pollination is by moths, ants or other insects.
The sepals, alternating with the petals, may be hairy.
The corolla has a short tube and lobes that flare out like a star but sometimes curve back.
Petals are thick and fleshy and may be very hairy.
At the centre is a coloured, fleshy, 5-part staminal corona.
The lobes are attached to the column formed by the fused stamen filaments.
The column surrounds the ovaries and styles.
The fused stigmas and anthers form a gynostegium.
Pollen in each of the 2 anther sacs or theca is massed into solid oblong or ovate pollinia.
The anthers have a membranous terminal appendage.
The theca of adjacent anthers are connected by 2 arms (the retinaculum).
With the corpusculum (gland) this forms the translator apparatus.
Most species produce a lot of nectar from a gland inside each staminal corona lobe.
The fruit are long cylindrical or fusiform, paired follicles.
The flattened seeds have a tuft of hairs at one end.
Many species have adapted to form a mutually beneficial relationship with ants.
Some ants make homes in variously modified leaves, others in the roots.
Hoyas are popular house or garden plants.
Cultivars include differently coloured flowers or variegated leaves with pink or white.
J.F.
