I cant find any information about the etymology of this Hoya except that the generic name Erythrina is derived from the Greek word ερυθρóς (erythros), meaning "red", referring to the flower color of certain species.
This Hoya produces very beautiful red leaves so maybe that is why it is named erythrina.
It is discovered and described by Dr. R.L. Rintz in 1978. It is fairly rare in nature in the forests of Pahang and Selangor (areas similar to US counties, geographical divisions) where it is found at 400-700 m in altitude. It is said to be common but not abundant along rivers in the areas.
This plant is very slow to start growth but with time it will become established and then put on rapid growth. It loves to twine and climb often with long, at first, leafless stems. As leaves develop they are usually deep shades of green and bronze, maturing into rather rigid deep green long undulant leaves with even deeper green venation. The undersides of these leaves is a rich dull maroon to pink, The foliage is very distinctive and beautiful often splotched or marked on the surface with pink markings. You will want to grow this one for the foliage alone!
The pendant flower clusters are formed of convex umbels of buttery yellow flowers fussy on the part of the upper curved surface, this is set off with a slightly lighter pagoda shaped center. There is a warm undertone to the yellowish petals. The tip and the edges of the petals are turned under giving a squared off shape to the flowers.
This is a plant that most collectors will find very attractive, unique and desirable. Although it is a little slow to start it is one that is worth cultivating and being patient with.
Note: This is one Hoya that should not be over-potted nor over-watered. It might be that it will like more light than most Hoyas and probably good humidity, since it grows along streams where there is ample light.
Source: Hoya Handbook (1992) P. 69. D. Kloppenburg & A. Wayman. Hoya erythrina Rintz
Special Thanks to Ryu Cuerdo (Hoya Ryu) and Angeline Simmons (The Hoya Lane) for allowing me to use their photos.
Hoya erythrina of my friend in the Philippines
My Hoya erythrina here in New Zealand. This is the mumma plant of the cuttings I sold early this year. It is now growing a long vine.
The flowers. You will observe a clean, sweet, citrus fragrance from the blooms both day and night. This is a peculiar trait, since most Hoyas are fragrant at night or late evening only reaching a peak of fragrance the first night, then with successive, diminishing peaks the following nights.