Selected Species - by Peter Taylor

Aerangis luteo-alba

THE great orchid company of Sanders at St Albans in England certainly thought they were on a 'winner' when this handsome species was collected in Uganda and quickly sent to them. In the late 1880s Aerangis species and related genera such as Angraecum and Jumellea were considered by most English and Continental growers to have only white flowers and the discovery of an Aerangis with a beautiful red column was seen by Sanders as a commercial triumph. They named the orchid Angraecum mirabile and proudly showed it at the Royal Horticultural Society meeting in 1922. Their triumph turned to disappointment however as most of their plants died after a few years - more on this point later.

The genus Angraecumwas established by Reichenbach in 1865 in Flora. The name comes from the Greek aer (air) and angos (vessel) and refers to the elongated flower spurs, characteristic of the genus which is endemic in Madagascar and is also found in Africa and the Comoro Islands.

All Aerangis species are monopodial and most grow as epiphytes. Leaves are generally obtusely bi-lobed, broader towards the tip than the base and plants have a growth habit similar to a Phalaenopsis. Fred Hillerman (1986) states that "a characteristic common to the natural habitat of practically all species of Aerangis is that they grow not too far from watercourses .... and they are rarely found in regions where the annual rainfall is less than 1250mm (50 inches) ... most ... grow in varying degrees of shade"

The orchid named Angraecum mirabile by Sander had been previously described as Angraecum rhodostictum by Kraenzlin in 1896 from plants collected in Cameroon. Schlechter revised the taxonomy of Angraecoid species in 1918 and transferred the species of the genus to Aerangis. Joyce Stewart completed the taxonomic journey of the lovely little species in 1979 when she accurately considered it to be a variety of the Zairean species Aerangis luteo-alba, so I guess that correctly the name is Aerangis luteo-alba var. rhodosticta.

Aerangis rhodosticta has a wide distribution in Africa - Cameroon, Zaire, Uganda, Ethiopia, Somalia, Kenya and Tanzania, and grows in generally warm, moist conditions in forests along rivers. They are twig epiphytes, occasionally found on the trunks of trees. Charles and Margaret Baker in their cultural notes show that the species has a 'double wet - double dry' rainfall. The wet seasons occur in spring and autumn with winter the primary dry season and secondary dry season in summer. The 'guru', Fred Hillerman, maintains that careful watering is necessary to succeed with this species - misting at least five times a week except in winter - in hot weather, daily drenching is recommended.

I grow my plants in an open shade house in Port Macquarie where our winter minimum is approximately 5 deg. C. Certainly judicious watering is required to get the plants through winter in these less than optimum conditions..

I have had no success in growing Aerangis rhodosticta in pots in any type of medium. The five or six that I have prefer to be mounted on slim cork strips so that their strong, flat roots can experience rapid wet and dry conditions.

Unless you can provide a winter minimum of about 12 deg. C, watering must be closely monitored. Light mistings on sunny winter mornings are all that is needed.

We have had good success in growing plants imported in flask, but Joyce Stewart (1970) mentions that (in habitat)it is not difficult to find, but once collected it is not easy to establish it in cultivation She continues with "this species is disappointing ... in that it frequently grows very well for several years and then suddenly dies" Stewart considers that this is what naturally happens to this species

My plants, two of which are illustrated here, have been growing nicely for two years out of the flask and have the lovely flowers that are so eye-catching on the show bench. I can fully appreciate Frederick Sander's excitement when the newly imported species flowered for him in 1922; it certainly is a captivating little orchid which species enthusiasts should add to their collections.

Peter Taylor, Port Macquarie, NSW

©Copyright Peter Taylor and Australian Orchid Council Inc. 2017.

Originally published in "Orchids Australia" October 2007.