Vol. 7, #3
Pterostelma Section Hoyas
Anyone who has ever done any Hoya research is constantly pressured by amateur growers to tell them all about Sections. The result is that some of us succumb to the pressure and end up with egg on our faces. Degreed taxonomists appear to be solidly against dividing hoyas into sections and with good reason. I merely suggested some sectional divisions and have regretted it ever since because all I got was a lot of criticism and constant badgering (some of it deserved). It seems it will never stop. So, if you ever get the idea of writing me and asking me about sections, don’t expect a reply.
HOWEVER ---- There is one “section” that I’d like to talk about some more. That is the Pterostelma (Wight) Hook. f. Section, which is typified by Hoya acuminata Benth. ex. Hook. f.
J. D. Hooker published this species in 1883, in Flora of British India, vol. 4, page 53. On this same page, he created the “Section Pterostelma..” Hoya acuminata was the only hoya he included in this section; This publication was entirely in English (the Code did not require Latin until the mid-1930s). J. D. Hooker’s publication is as follows:
“SECT. H. Pterostelma. Corolla reflexed, lobes longer than broad. Column sessile, obconic; coronal processes laterally compressed, semi-cordate, 2-winged, with an erect subalate pointing the inner angle. Plocostemma, Bl.
2. H. acuminata, Benth. in
Quite glabrous. Stem stout, 1-2 ft., subscandent and
pendulous. Leaves 3 - 4 by 1 - 1½ in.,
elliptic-lanceolate, nerves obscure; petiole ¼ - ½ in. Umbels terminal and Axillary, few-fld.; peduncles ½ in., pedicels
1 in. Sepals
linear-oblong, obtuse, ciliolate. Corolla-lobes 1 in.,
glabrous, tube puberulous within.
As noted in the above publication, J. D. Hooker recognized Wight’s 1834 publication of the Genus Pterostelma acuminatum * which was typified by Wallich’s Cat. 8170*2
Note, also, that J. D. Hooker, the author of the Pterostelma Section placed the Genus Plocostemma into synonymy. I am sure that he did that because he knew that the Genus Plocostemma was not published until 15 years after Wight’s publication of the Genus Pterostelma and its type, Hoya lasiantha is almost identical, in the features that count, to Pterostelma acuminata. The coronas are extremely similar as are the corollas except for the wooly area at the base of the coronas.
*Although Hooker f. spelled it acuminatum, Wight spelled it acuminata in his publication.
*2 Wight cited Wall. Asclep. #129. This is the same as Wall. Cat. 8170. The specimen bears both numbers. All of Wallich’s specimens appear to have been given two numbers.
Here is a translation Wight’s description of the Pterostelma Genus and it type, Pterostelma acuminata Wight:
Wight. Calyx 5-parted. Corolla
To the above, Wight added, in English: “This genus is allied to Hoya both in habit and in the structure of the flowers, differing principally in having foliaceous in place of fleshy crown-leaves, and in the dorsal not lateral attachment of the pollen masses to the corpuscle.
1. P. acuminata (Wight). – Wall.! Asclep. N. 129 (absque nominee)* --In Silhet; Wallich.
My specimens do not possess a perfect umbel. –(R. W.)
* = Without a name.
E-mail critic #1: “You are wrong about this and Hoya lasiantha being Pterostelmas because Wight said that the corollas are rotate.”
My reply: So he did, but he also said that he did not possess a perfect umbel.
I was unable to find a flower picture on the Wallich
specimen but the above picture of a single flower on the Hooker f. type shows a
rotate flower. This flower is rotate due
to stage of development at the time it was pressed and dried.
You need to be aware that when an author publishes a species name based on a pressed and dried herbarium specimen, he often has only about 2 feet of plant stalks with its attached leaves and flowers. Sometimes the leaves are detached and in a pasted on envelope, as are the flowers. When the flowers are present they are often flattened and they are sometimes in various stages of maturity. All the hoyas I’ve observed (n more than 50 years of growing them) close their flowers before falling off. Even those with reflexed flowers don’t open up completely reflexed. They open in stages and when their time is up they reverse the order and close in stages. Whatever stage a flower was in when the specimen was mounted and pressed is the stage the author of this type of specimen will see and describe. If a full umbel (or more than one umbel) is present, the author is likely to see flowers in all stages of maturity but if, as Wight said, there is not a perfect umbel present, there is no way the author can be sure is the flowers are rotate, campanulate, recurved, reflexed or revolute. J. D. Hooker had seen the Wallich specimen and had collected material from the same area so his specimen gives us a better picture.
made my own picture of a specimen I found at Arnold Arboretum (
The above is a slightly reduced portion of the holotype specimen of Hoya myanmarica P. T. Li.
It is F. Kingdon-Ward #21190. The sketch in the bottom right corner is a sketch I made of one of its flowers while looking at it through a microscope. I was able to do that when I had the Arnold Arboretum (Harvard) collection on loan in the mid-1980s.
Hoya myanmarica P. T. Li is a synonym for Hoya acuminata (Wight) Benth. ex. Hook. f.
This makes Hoya acuminata the correct name because it came first. Hoya acuminata was published in 1883; Hoya myanmarica was published in 1994.
On the lower half of the Hoya myanmarica holotype specimen, Kingdon-Ward wrote some descriptive words that do not appear in P. T. Li’s description, nor in J. D. Hooker’s. Those words are, “An epiphytic shrub, the flowering branches erect, eventually as they grow longer, flopping and hanging. Flowers snow white, the long corolla lobes completely reflexed.” Note that Wight was uncertain if this were a twining shrub or a decumbent plant.
The three specimens (Wight’s type; Hooker f.’s type and P. T. Li’s type) remind me of Hoya javanica and somewhat of Hoyas cumingiana and densifolia but what a great difference its flowers are. These flowers measure up to and sometimes more than two inches in diameter!
The following is the late Hon. Douglas H. Kent’s take on the subject as noted in a manuscript he and I were working on at the time of his death:
“Hoya acuminata (Wight) Benth. ex Hook. f., Fl. Brit.
Pterostelma acuminata Wight, Contr. Bot. Ind. 39 (1834). (Lectotype:
Cyrtoceras acuminatum Regel, Cat. Pl. Hort. Aksakov. 46 (1860), nom. nud. Hoya griffithiana Decne. ex. Hook. f. (1883).
In Syn. Hoya myanmarica P. T. Li 1995).
Illustration: Hoyan 12(4): 96 1991).”
WHERE CAN ONE GET CUTTINGS OF PLANTS
OF THIS SPECIES? At the present time (January
2009) it is not yet in circulation, unless it is being distributed under a
different name. Hoya collectors appear to have been collecting in every known
A new hoya book: The Genus Hoya by Anders Wennström and Katarina Stenman.
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