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Heavenly
Hoyas
An introduction to the species
of Singapore and Malaysia
Text by Leong Lup San
Photos by K. F. Yap
Most people
will associate Hoya with the common garden species H. carnosa
from China, a vine with white to pink waxy umbels of flowers, as
well as its cultivar known as "Indian Robe" or "Crinkled Curl".
The genus Hoya is much more than these in terms of the forms, leaves,
sizes and flowers.
This may come as a surprise for some but academics have named up
to 200 species, with the actual number fluctuating up and down over
the years as some species are merged while new ones are described.
Hoyas belong to the family Asclepiadaceae, which contain
many horticulturally interesting plants like the Stapeliads. Usually,
hoyas are twining vines, ooze milky sap when cut (there are exceptions),
and more often than not, have interesting waxy blooms. The umbel
of flowers are borne out of the peduncle, a thick flower stalk that
does not drop off after flowering is over. In fact, it can grow
bigger and more flowers can arise the next time round. In the wild,
hoyas normally inhabit shady tropical forests but there are succulent
forms found in the deserts of Australia.
The regions with the most hoya species are Southeast Asia and the
island of New Guinea. According to RE Rintz (1978), Peninsular Malaysia
has about 25 species out of which nine are also found in Singapore
(Hsuan Keng, 1990). The nine species is inclusive of Physostelma
wallichii, now reclassified as Hoya campanulata (Rintz,
1978). Even though some of the Singapore records are very old, I
have seen H. verticillata, H. latifolia and H. diversifolia
growing wild in mangroves and forests on the mainland and there
is no doubt that more of the missing species are to be found here.
Local Species
Singapore and Malaysia house one of the species with the largest
leaves—up to 25 cm long. This is called H. latifolia but
also known as H. macrophylla and H. polystachya. It
has thick, pretty heart-shaped leaves with prominent venation; alas,
the individual flower is rather inconspicuous. Clumps can be found
growing within and around the Zoological Garden in Mandai and it
inhabits a drier habitat. There is an elegant long-leafed form found
across the Causeway in Malaysia.
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Hoya diversifolia
Hoya macgillivrayii
Hoya multiflora
Hoya verticillata
Hoya pubicalyx
from the Philippines
Hoya pachyclada
hails from Thailand
Hoya kerrii
from Thailand |
 Hoya
lasiantha Korthals ex Miquel (1856)
Text and photo by K. F. Yap
On April 13-16 this year, I joined a group of 31 nature lovers on
a trip to the Endau-Rompin National Park in Johor, Malaysia. The trip
was organised by S. Rajamanickam on behalf of the Nature Society (Singapore).
On April 15, a group of us ascended Gunung Janing Barat (450 metres
above mean sea level). It was a gruelling climb, even though I had
hired a porter (Dolah, a young Jakun tribesman) to help carry my heavy
camera equiprnent. We were the last climbers to reach the sandstone
plateau, home to the endemic Livistona endauensis and peat
swamp forests. L. endauensis, a fan palm species, was first
found in Ulu Endau, Johor.
The descent was even more treacherous than the ascent. About halfway
down, while catching our breath, I spotted, in the distance, a hanging
patch of orangey-gold swaying in the afternoon breeze. On approaching
closer, it turned out to be a Hoya species (Asclepiadaceae) that I
had never seen before.
It was truly an exquisite encounter of the first kind. I have recorded
the image for posterity.
The epiphytic plant of five branches, arising from a single stem,
was growing out of a tree wound, at about eye-level. One of the pendulous
branches carried an umbel (inflorescence) of four blooms. They were,
as described by Rintz (1978), positively-geotropic (hanging earthwards).
The pointed corolla lobes were strongly reflexed, densely pubescent
with long straight hairs only at the base and golden orange. The corona
lower lobes were upcurved and roundly blunt, white tinged with light
pink.
Rintz (1978) recorded it as uncommon in the lowland and hill forests
of Perak and Selangor, Peninsular Maiaysia. It was not recorded as
having been found in the State of Johor, West Malaysia. Hoya lasiantha
is, indeed, alive and well in its newly discovered habitat. Nature
lovers do sometimes get unexpected and surprising rewards.
Acknowledgement
I am indebted to Chuah Ai Lin for digging up a copy of Rintz's publication
from the NUS Library. |
Another
Hoya species, which one can find in the jungles of MacRitchie Reservoir,
is a smaller vine which is very floriferous and gives off an intensely
sweet smell in the evening. It grows very well in apartment balconies
and deserves more attention. The plant has been called H. parasitica,
H. ridleyi, H. globifera and H. acuta before settling into
the present H. verticillata. This has a very wide distribution—from
India, Indo-China to Malesia.
Near the coast and in mangroves, another large vine with pale green
succulent leaves and typical waxy pink blooms can be found. Its name,
H. diversifolia, remains unchanged over time.
There are even myrmecophilous hoyas; H. mitrata (not recorded
in Singapore) has two types of leaves, the typical speckled hoya leaf
and the "cabbage-type" leaves which function as ant nests. Another
ant-plant, H. imbricata from the Philippines, has pairs of
disk-shaped leaves cupped against tree trunks which act as ant "hotels".
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Non-Conformists
According to Hsuan Keng (1990), H. coronaria is also found in Singapore.
This is a very different plant—dark green hairy stems and leaves, with
very large thick white waxy flowers. It belongs to the Eriostemma section
which some taxonomists may place in a genus on its own, owing to features
very distinct from the "normal" hoyas. It is certainly a shy bloomer, but
very rewarding when it does.
Physostelma wallichii is also another plant which sits on the fence—it
is more popularly called H. wallichii or H. campanulata. Vegetatively,
it looks like a skinny vine with soft green leaves. Its flowers are like
waxy bells instead of the usual "star" shape. It was recorded in Tampines
years ago but I suspect it has gone extinct by now. Currently, this plant
is placed in the section Physostelma with several other species, so it is
still a hoya—for now at least.
Taxonomists have also threatened to remove H. multiflora (the shooting
star hoya) from the genus and one can understand why—it is a shrub
(not a vine) with a truly unique bloom. This plant has not been recorded
wild in Singapore.
Personally, I think an introduction to hoyas cannot he complete without
mentioning two other very interesting species. The first one, H. imperialis,
is a large thick vine and is truly regal when it blooms. There are many
colour variants, from bright to purplish red and even white. It is found
in Malaysia and Borneo.
Another hoya is called H. macgillivrayii—from Northern Queensland
and New Guinea. There are several similar species like H. onychoides
and archboldiana—all equally impressive. Their blooms, among
the largest in the genus and certainly one of the most perfectly formed,
epitomise the beauty created via eons of evolution in the natural world.
Literature cited
- Rintz, R. E. (1978). The Peninsular Malaysian Species of Hoya (Asclepiadaceae).
Malay. Nat. J. 30 (3/4): pp 467 - 522.
- Keng H. (1990). The Concise Flora of Singapore (Gymnosperms &
Dicotyledons). pp 148 - 149.
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