Dregeas come from Asia and are evergreen in the wild, but if you keep them in your greenhouse with low winter temperatures, they will lose most of their leaves. They are also known under their synonym Wattakaka sinensis.
It is a climbing plant that will flower every spring with white flowers that have a splash of pink in the centre. They are highly scented, which usually means in these type of plants that they are moth-pollinated. The flowers last for up to a week and resemble hoya flowers. Not surprising as Hoyas and Dregeas are related. Another asclepiad species that has highly scented moth-pollinated flowers is Araujia sericifera, although the flowers on that plants do not resemble Dregea flowers.

Dregea sinensis

Dregea sinensis

As with Hoyas, Dregeas rarely set seed in the greenhouse, but when they do, they form twin-seed horns which will burst open when ripe and can contain up to 50 seeds. The seeds remain viable for up to a year, but it is better to sow them as soon as possible. If you sow them straight away, you will get almost 100% success; if you leave it till 3-6 months, you will get 25-50%; and after a year, you may only get one or two to germinate.
The leaves are heart-shaped and fairly large. It is possible to propagate this plant by cuttings, preferably in the spring. I use cuttings with two nodes, one for the roots and one for the new growth, just as you would do with Hoyas. They can be grown in shade or full sun and will grow outside in the summer. They can have a bit of frost (-2 or 3°C), but it is better to give them some protection.