Notes on the Marsdenieae (Asclepiadaceae)--A new, unusual species of Hoya from Northern Borneo

7 Pages·1996·2.8 MB·

by  R Omlor

Notes on Marsdenieae (Asclepiadaceae)—A New, Unusual Species
of Hoy a from Northern Borneo
Ralf Omlor
Universitat Kaiserslautern, FB Biologie, Abteilung Systematische Botanik, Postfach 3049,
67653 Kaiserslautern, Germany
Abstract. Hoya telosmoides R. Omlor sp. nov. have been transferred from the Marsdenieae to oth¬
from northern Borneo is described and illustrated. er tribes:
Its systematic position is discussed, and an intro¬ The delimitation of the Stapelieae by means of
duction is given to the major subgroups of the the pellucid germination zone on the apex or inner
Marsdenieae and their delimitation. side of the pollinia resulted in the transfer of Ten¬
aris E. Meyer (Brown, 1902), Heterostemma Wight
The following description of a new species of & Amott (Schill & Jakel, 1978; Bruyns & Forster,
Hoya R. Brown has resulted from my work on a 1991), Pentasachme Wallich (Bruyns & Forster,
generic revision of the tribe Marsdenieae in Ascle¬ 1991), and Swynnertonia S. Moore (Liede & Albers,
piadaceae. Since the attribution of this new species 1994) from the Marsdenieae to the Stapelieae. For
to the genus Hoya is not self-evident, and since at the same reason the genus Emplectanthus N. E.
present there is no consensus as to how most genera Brown should also be transferred to the Stapelieae.
of the tribe are to be defined, it is necessary to give The minute pollinia of this genus have an apical
a short introduction on the delimitation and the ma¬ germination mouth, and the corona consists of sta-
jor subgroups of the Marsdenieae. minal lobes and additional interstaminal, pouch¬
In a broad taxonomic sense the Marsdenieae like segments. Terminal anther appendages are
comprise some 500 species in about 60 genera (a lacking. N. E. Brown (1902) already described
list of all validly published generic names can be these characters, but placed the genus in the Mars¬
found in Liede & Albers (1994)), which are dis¬ denieae because it resembles some species of Ty-
tributed throughout the tropical and subtropical lophora R. Brown in habit very closely. Brown
regions of the world. The taxonomic delimitation of (1902) argued that Emplectanthus might be a ge¬
the group is difficult and the tribal concept—as neric hybrid between Tylophora and Riocreuxia De¬
well as the tribal name—has been subject to re¬ caisne, but there is no evidence for this hypothesis.
peated change (e.g., Endlicher, 1838; Decaisne, The genera Rhynchostigma Bentham (Brown,
1844; Bentham, 1868, 1876; Schumann, 1895). At 1902) and Trichosandra Decaisne (Friedmann,
present the Marsdenieae are circumscribed within 1990) were transferred from the Marsdenieae to the
subfamily Asclepiadoideae by longitudinal dehis¬ Secamoneae in subfamily Secamonoideae.
cence of the thecae, erect or ascending pollinia, Only recently Kunze et al. (1994) pointed out the
and anthers with membranous terminal appendages isolated position of Fockea Endlicher and Cibirhiza
(Bruyns & Forster, 1991). With exception of the Bruyns within the Marsdenieae and established the
membranous anther appendages these characters new tribe Fockeeae to accommodate them. Both
also apply to the Stapelieae, but the latter can be genera are distinguished from the Marsdenieae by
distinguished by the pellucid germination zone on their sometimes large tuberous rootstock, by the
the apex or the inner side of their pollinia, (Bruyns complexity of their corona, and by the primitive
& Forster, 1991). Delimited by this differentiation state of their translator to which the pollinia are
of the pollinia, the Stapelieae sensu Bruyns & For¬ directly attached, instead of being linked via cau-
ster are almost certainly a monophyletic group. In dicles as is the case in all other members of the
sharp contrast, the Marsdenieae cannot be defined Asclepiadoideae (Kunze, 1993). An important de¬
by synapomorphies; instead, they have always been viation from Asclepiadoideae not mentioned by
a conglomeration of several generic groups that do Kunze et al. (1994) is that in Fockea and Cibirhiza
not necessarily belong together. Since the last com¬ the pollinia are composed of rhomboidal and T-sha¬
plete generic revision of the Marsdenieae (Schu¬ ped pollen tetrads. In this respect the Fockeeae
mann, 1895) about 37 new generic names have agree with the Periplocaceae and Secamonoideae
been attributed to the tribe and a number of genera (commonly regarded as the most primitive groups
Novon 6: 288-294. 1996.
Volume 6, Number 3 Omlor 289
1996 Notes on Marsdenieae
of Asclepiadaceae s.l.), whereas the Asclepiadoi- pellucid germination zone on their outer margin
deae generally are characterized by linear pollen (Schill & Dannenbaum, 1984).
tetrads as the result of two successive meiotic di¬ The most prominent representative of this sharp¬
visions (Safwat, 1962). This observation substanti¬ ly distinguished group is the genus Hoya\ in the
ates the hypothesis of Kunze et al. (1994) that the following sections I will refer to these “derived”
Fockeeae represent the most primitive group within Marsdenieae informally as the “Hoya group.” Be¬
the Asclepiadoideae. sides the large genus Hoya, which is here under¬
Despite all these rearrangements, the Marsden¬ stood in the broad taxonomic sense circumscribed
ieae still include some genera that do not fit com¬ by Forster and Liddle (1990) (thus including Phy-
fortably within the tribe. The reason for this lies in sostelma Wight and Cyrtoceras Bennett), the group
the vague delimitation from the Asclepiadeae, further comprises Absolmsia spartioides (Bentham)
which is entirely based on the orientation of the Kuntze, a highly specialized epiphytic subshrub
pollinia: “erect or horizontal” in Marsdenieae ver¬ from Borneo (see Gilbert et al., 1995: 14), and in
sus “pendulous” in Asclepiadeae (Bruyns & For¬ my view Micholitzia obcordata N. E. Brown, which
ster, 1991). The pendulous position of the pollinia was recently reviewed by Goyder and Kent (1994).
is generally regarded as the apomorphie state (e.g., The monotypic, little known Malesian genera Or-
Wanntorp, 1988: 21), but the transition from erect eosparte Schlechter and Heynella Backer might also
to pendulous pollinia may have occurred several belong here, but this still has to be confirmed.
times in the evolution of Asclepiadoideae. Apart Although clearly differentiated from the rest of
from the Gonolobeae, which are probably derived the Marsdenieae, the Hoya group is not equal in
from the Asclepiadeae, almost all genera with an rank to the Stapelieae. Whereas all the important
intermediate condition (i.e., caudicles attached lat¬ characters of the Stapelieae (pollinia with apical
erally in the middle part of the pollinia) or with germination mouth, corona consisting of staminal
variable orientation of the pollinia have been at¬ and interstaminal segments, succulent stems, lack
tributed to the Marsdenieae. These “intermediate of membranous anther appendages) do not occur in
genera” fall into two apparently unrelated groups, the Marsdenieae, the characters which in combi¬
namely the Tylophora group in the Old World, and nation distinguish the Hoya group can individually
a group of New World genera at least consisting of be found—to varying degree and in various
Barjonia Decaisne, Nephradenia Decaisne, Jobinia states—in other Marsdenieae too:
Fournier, and Vailia Rusby. Though crucial for an Epiphytic life form, herbaceous growth, fleshy
understanding of the phylogeny of Asclepiadoideae, leaves, and spindle-shaped, unmargined seeds are
the affinities of all these “intermediate genera” are also characteristic of the genus Dischidia R. Brown
poorly understood. and its segregates. With regard to floral characters,
If these “intermediate genera” are left aside, however, the Dischidias are not fundamentally dif¬
eventually the “natural core” of Marsdenieae re¬ ferent from the “basal” Marsdenieae (e.g., Mars-
mains. It is primarily a group of woody perennial denia tinctoria R. Brown).
lianas or twining shrubs with simple staminal cor¬ Persistent, racemiform contracted inflorescences
onas (rarely a coralline corona), undifferentiated, occur in several Southeast Asian Marsdenieae (e.g..
erect, elongated pollinia, and flattened, comose, Dischidanthus urceolatus (Decaisne) Tsiang, Gon-
sometimes broadly margined, smooth seeds. Rep¬ gronema wallichii Decaisne, Thozelia racemosa F.
resentatives of this basal type of Marsdenieae are Mueller ex Bentham, Clemensiella mariae (Schle¬
found throughout the warmer regions of the world. chter) Schlechter, and probably all Dischidia spe¬
A second, more advanced group is confined to cies).
southern Asia, Malesia, and Australia. This group Resemblances to the floral characters that most
mainly consists of herbaceous vines or climbing or sharply distinguish the Hoya group can be recog¬
dependent epiphytes with often fleshy leaves and nized in the genus Telosma Coville. In many, if not
persistent inflorescences that produce flowers for all, Telosma species the outer margin in the lower
several seasons. The corona lobes in this group are half of the pollinia is strongly flattened (sometimes
staminal, often horizontally spreading, and gener¬ even pellucid) and generally curved forward (to¬
ally consisting of an inner tip that is appressed to ward the anthers). This type of pollinia can be re¬
the anthers and a variable outer part with revolute garded as intermediate between the undifferentiat¬
lateral margins. The seeds are comose, spindle- ed pollinia of all other “basal” Marsdenieae and
shaped, and lack differentiated margins, and the the derived pollinia of the Hoya group. Apart from
pollinia—this is the most significant deviation from the pollinia, there also are similarities concerning
the rest of the Marsdenieae—have a conspicuous. the construction of the staminal corona. In Telosma
290 Novon
the corona consists of laminar lobes, which adaxi- slightly recurved. Gynostegium ca. 4.5 mm high,
ally bear a filiform appendage (Liede & Kunze, almost completely filling the corolla tube. Corona
1993: fig 2A). From this model the complex corona staminal, fleshy, slightly spreading, about as high
of the Hoya group can easily be derived by the as the sterile part of the stamens; corona lobes con¬
recurvation of the lateral margins of the laminar nate with the back of the stamens, adaxially elon¬
segment and the shift in its orientation from erect gated into a free, ovate tip about 0.4 mm long which
to horizontal. is appressed to the stamens, lobes laterally com¬
Concerning its vegetative characters, however, pressed, abaxially broadened into a massive erect
Telosma is exceedingly different from the members process with revolute lateral margins and truncate
of the Hoya group. The Telosma species all are apex; the corona lobes with a finely striated, hard
woody climbers with thin, cordate leaves, salver¬ surface. Anthers erect, terminated by an ovate hy¬
shaped flowers, and flattened, broadly margined aline appendage, ca. 1.5 mm long, with rounded or
seeds. With respect to these characters a close re¬ retuse-bilobed apex. Pollinia erect, oblong-obovate,
lationship between these plants and the Hoya group compressed, 0.7 X 0.3 mm, with a lateral “pellucid
appears rather unlikely. Their vague similarities margin.” Corpusculum 0.45 X 0.28 mm. Carpels
with the Hoya group would perhaps deserve no at¬ glabrous, style head with short conical appendage,
tention, were there not a Hoya species with a Te- not exceeding the anthers. Fruits and seeds un¬
losma-like corolla. known.
Because of its unusual corolla Hoya telosmoides
Hoya telosmoides R. Omlor, sp. nov. TYPE: Ma¬
does not at first sight look like a true Hoya. Instead
laysia. Sabah: Mt. Kinabalu, Tenompok, 1500
it might be taken for a Dischidia or a Telosma spe¬
m, 7 June 1932, Clemens 29828 (holotype,
cies, or for a near relative of Gongronema filipes
BM; isotype, K). Figures 1, 2.
Kerr, which superficially resembles it very closely.
Ab omnibus speciebus Hoyarum adhuc cognitis corolla However, the herbaceous growth, the fleshy elliptic
tubo urceolato intus villoso, fauce contracto, segmentis pa- leaves, and the umbelliform inflorescence with
tentibus linearibus-triangularibus recedit. scars of previous flowers indicate a relationship
Herbaceous glabrous vine. Stems twining, cylin¬ with the Hoya group. This is fully confirmed by the
drical, about 3 mm diam.; intemodes 8-25 cm long. floral characters. The gynostegium (Fig. 1C), though
Leaves opposite, petiolate; lamina narrowly elliptic superficially similar to that of Gongronema filipes
or elliptic-oblanceolate, shining, (80-)100-130 X Kerr or Gongronema wallichii Decaisne, reveals all
(25-)30-55 mm, coriaceous, apex acuminate or at¬ the typical characters of the Hoya group: The co¬
tenuate, base acute or cuneate, with a pair of glands rona is solid, with a finely striated surface, and the
at least when young, margin slightly revolute, the abaxial lobes have revolute lateral margins (Fig.
midrib clearly elevated on the lower surface, sec¬ ID). In the older literature the last character often
ondary venation less conspicuous, consisting of 4— is simply described as “corona lobes dorsally sul-
7 brochidodromous veins branching from the mid¬ eate.” However, very many corona lobes are sul-
rib at a wide acute or an almost right angle; petiole cate,” at least in their basal part; the crucial point
8—13 mm long. Inflorescences occurring singly at is whether the furrow results from revolute margins,
the nodes, clearly interpetiolar, long pedunculate as this serves to distinguish the Hoya group from
(40-55 mm), pendulous, umbelliform with up to ca. other Marsdenieae.
18 flowers, persistent, rachis with scars of previous Together with the peculiar construction of the co¬
flowers; pedicels 15—20 mm long, glabrous. Flowers rona lobes, the shape of the pollinarium (Fig. 1A)
10-15 mm long, up to 20 mm diam. Sepals lan¬ unequivocally places this new species in the Hoya
ceolate-ovate, 2 X 0.8 mm, apex rounded, alter¬ group. Elongated, compressed pollinia with the
nating with single glands, glabrous. Corolla fleshy, characteristic germination zone along the entire
having an inflated tube that is slightly constricted outer margin do not occur elsewhere in the Mars¬
at its top, and bearing five narrowly triangular, erect denieae (see above), and the shape of the corpus
or slightly spreading lobes, outside glabrous, pale culum with the caudicles attached in the middle
yellow tinged with purple; corolla tube 5.5-6.5 mm part likewise is typical of the Hoya group.
long, inside densely covered with long unicellular, While the incorporation of the new species in the
recurved trichomes, at its base bulged between the Hoya group is thereby strongly supported, its affin
calyx lobes, the throat narrowed (almost segmented) ities within that group are much more difficult to
by infolds below the sinuses of the petals; free co¬ assess. A modem, complete revision of Hoya, whic
rolla lobes up to 10 mm long, glabrous, margins probably comprises over 100 species, is not avail
Volume 6, Number 3 Omlor
1996 Notes on Marsdenieae
HIl
HlI
Itll
m
m
5
2.
c
1mm
Figure 1. Hoya telosmoides R. Omlor. —A. Pollinarium. —B. Flower. —C. Gynostegium.
stamen, corona lobe sectioned to illustrate the revolute margins. All drawn from Clemens 30259.
F
igure 2 292
.
H
olotype o
f H
oya telosm
oides (C
lem
ens 2
9
8
2
8
(B
M
)). No
v
o
n

iiiiJilli'iiiiliiiJ.'iiiliiiiiiii •iiiifiiifliiiiiiiiiliiiiliitrliiiiffiiflfi/ffmilHii l
Volume 6, Number 3 Omlor 293
1996 Notes on Marsdenieae
able, and neither the delimitation nor the infrage¬ multiflora. I have been unable to locate any mate¬
neric classification of the genus has yet been sat¬ rial of Oreosparte celebica. The holotype (Schlechter
isfactorily resolved. Important recent contributions 20512) was apparently destroyed along with the
to the taxonomy of Hoya are provided by Rintz’s major part of the Berlin Herbarium in 1943 (Hiep-
(1978) revision of the Malaysian species and by ko, 1978; Nicholas, 1992). From Schlechter’s As-
Forster and Liddle’s (1990) treatment of the Aus¬ clepiadaceae collection at B only a few Hoya atid
tralian species. In both accounts Hoya is treated in Dischidia specimens remained (Hiepko, pers.
a broad taxonomic sense, including the somewhat comm.). However, the plant must have been rather
deviating Physostelma Wight (= Hoya campanulata common in the mountains of Minahassa, since
Blume group) and Cyrtoceras Bennett (= Hoya Schlechter (1916) reported that its filiform stems
multiflora Blume). have been used to bundle the collections during the
In this broad taxonomic sense the genus Hoya expedition. Therefore it may be assumed that du¬
shows a wide variation in floral characters: Whereas plicates had been collected and distributed to other
most species of the genus have flowers with a deep¬ herbaria. It would be appreciated if any information
ly lobed rotate, often reflexed corolla, a few species, concerning the existence of such isotypes were to
e.g., H. campanulata Blume, have broad-campan- be eommunicated to the author.
ulate flowers. A small number of species are ex¬ The second monotypic genus that might be re¬
ceptional in having pollinia lacking the typical ger¬ lated to Hoya telosmoides is Heynella Backer from
mination zone otherwise characteristic of the Hoya Java. Heynella lactea Backer, according to the de¬
group. These are H. mitrata Kerr (Rintz, 1978) and scription, is characterized by a salver-shaped co¬
a group of species—such as H. coronaria Blume rolla with a flask-shaped tube, and ovate-oblong,
(Rintz, 1978: 505) or H. lauterbachii Schumann slightly spreading lobes (Bakhuizen, 1950). It is
(Forster & Liddle, 1990: 220)—which Schlechter distinguished from Hoya telosmoides by its epi¬
(1914) united in his section Eriostemma. Hoya pus- phytic nonclimbing habit and by terminal inflores¬
ilia Rintz differs by atypical corona lobes that lack cences (a rather doubtful observation). Further¬
the characteristic revolute margins. These are only more, in contrast to Hoya telosmoides the free lobes
a few, notable examples for Hoya species with de¬ of the corolla are considerably shorter than the co¬
viating characters. Rintz (1978) described in detail rolla tube. Unfortunately, the type material of Hey¬
the morphological variation present in Hoya. nella lactea, located at BO, Indonesia (Forster &
If the genus Hoya is accepted in the broad tax¬ Liddle, 1994), could not be sent on loan for study.
onomic sense circumscribed by Forster and Liddle Neither in the case of Oreosparte nor in Heynella
(1990), the new species presented here can casu¬ can it be judged from the protologue whether the
ally be ascribed to it. Although differing by the pollinia have the lateral pellucid germination zone
shape of its corolla from all hitherto known species and whether the corona lobes exhibit the charac¬
of Hoya, H. telosmoides entirely agrees in the re¬ teristic revolute margins. For the time being, the
maining diagnostic characters of the genus. It must taxonomic position of these genera within the Mars¬
be considered that species with campanulate flow¬ denieae must therefore remain uncertain.
ers and the above-listed species with more funda¬ At present Hoya telosmoides is known only from
mental deviations are (well founded) commonly ac¬ two areas in northern Borneo, where it is found
cepted in Hoya. Within Hoya the new species twining in lower and upper stories of mountain for¬
occupies an isolated position and should therefore est, at altitudes of 800-1500 m.
be classified in a separate section.
Paralypes. MALAYSIA. Sabah: Ml. Kinabalu. Tenom-
It has to be mentioned that two monotypic genera pok 1500 tn. 15 June 1932, Clemens 30259 (K): Ml. Kin¬
of uncertain affinities might be related to Hoya te¬ abalu. Penibukan, 1200-1500 m, 10 Jan. 1933, lop of 80
losmoides. One of these, the genus Oreosparte, was ft tree. Clemens 30868 (BM). Sarawak: Gunong Api, ulu
established by Schlechter (1916) for an exception¬ Melinau. Tuloh. Baram District. NE flank of mountain.
4°07'N, 115°15’E, 880 m. 30 Sep. 1971. “small climber
al, Hoya-like species he had collected in the moun¬ in understorey, inflorescence pendulous, corolla pale yel¬
tains of Minahassa on Celebes. This species, Or¬ low, waxy, corona sunk, anthers reddish brown,” Anderson
eosparte celebica Schlechter, is described as having 30815 (K).
a campanulate, inside minutely pubescent corolla
Acknowledgments. The present contribution re¬
tube with a contracted throat and lanceolate,
sulted from my ongoing work on a generic revision
spreading lobes. Apparently Oreosparte concurs
of Marsdenieae and is based on the examination of
with Hoya telosmoides in shape of the corolla, but
herbarium material of some 200 species borrowed
it is described as having a stalked gynostegium and
a corona similar in shape to the corona of Hoya mainly from B, BM. HBG. K. M. and P after ex-
294 Novon
tensive study of their collections; individual spec¬ du genre Trichosandra Decne. (Asclepiadaceae). Bull.
imens have been provided by IBSC, L. and US. A Mus. Natl. Hist. Nat., B, Adansonia 12: 131-138.
Gilbert, M. G., W. D. Stevens & Li Ping-tao. 1995. Notes
list of the specimens examined is available upon on the Asclepiadaceae of China. Novon 5: 1-16.
request. I am indebted to the directors of the cited Goyder, D. J. & D. H. Kent. 1994. Micholitzia obcordata
herbaria for permission to study their collections N. E. Br. (Asclepiadaceae—Marsdenieae) reinstated.
and for sending specimens on loan. Furthermore, I Asklepios 62: 13-19.
Hiepko, P. 1978. Die erhaltenen Teile der Sammlungen
express my gratitude to Herbert Huber, under des Botanischen Museums Berlin-Dahlem (B) aus der
whose guidance this work was done. My sincerest Zeit vor 1943. Willdenowia 8: 389-400.
thanks also go to David J. Goyder for valuable dis¬ Kunze. H. 1993. Evolution of the translator in Periplo-
cussions and suggestions, to Wolfgang Stuppy for c1a2c2e. ae and Asclepiadaceae. PI. Syst. Evol. 185: 99-
critically reading the manuscript, and to Andreas Kunze, H., U. Meve & S. Liede. 1994. Cibirhiza alber-
Stem for taking the photograph of the holotype. siana, a new species of Asclepiadaceae, and establish¬
This work was supported by a grant from the ment of the tribe Fockeeae. Taxon 43: 367—376.
Liede, S. & F. Albers. 1994. Tribal disposition of genera
LGFG-Kommission Rheinland-Pfalz.
in the Asclepiadaceae. Taxon 43: 201-231.
-& H. Kunze. 1993. A descriptive system for co¬
rona analysis in the Asclepiadaceae. PI. Syst. Evol. 185:
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