Dendrobium annulatum Juswara, Schuit. & Champion, 2019

Juswara, Lina S., Schuiteman, André & Champion, Jeffrey, 2019, Dendrobium annulatum (Orchidaceae: Epidendroideae), a new species of Dendrobium section Grastidium from Indonesian New Guinea, Phytotaxa 414 (3), pp. 151-155 : 151-154

Dendrobium annulatum Juswara, Schuit. & Champion , sp. nov. ( Fig. 1–3 )

Type :— INDONESIA. New Guinea, without locality data, cultivated plant, February 2016, Champion WP 14 (holotype: BO!, spirit; isotypes: BO!, dried specimen, K!, spirit) .

The leaf-sheaths are similar to those of Dendrobium gjellerupii Smith (1911: 4) in being distinctly warty, but in D. annulatum the warts are more irregular and larger and the apical part of the sheath is swollen into a smooth ring; this ring-like swelling is absent in D. gjellerupii . Florally, D. gjellerupii differs in the abaxially warty sepals and the subentire, not distinctly trilobed lip. The flowers of D. annulatum are more similar to those of D. goodallianum de Vogel, Winkel & Vugt (2014: 87) , but this has a far less densely hairy midlobe with thinner hairs, obliquely truncate (not acuminate) side lobes and different colours (white tinged lilac in D. goodallianum , golden yellow in D. annulatum ). The peduncle of D. goodallianum emerges well beyond the spathe, whereas it is hidden inside the spathe in D. annulatum . In D. goodallianum , the inflorescence arises from the bare stem below the leaf-sheath above the nearest leaf, whereas in D. annulatum it breaks through the leaf sheath below the nearest leaf. Vegetatively, D. goodallianum differs in the smooth leaf sheaths without a ring near the mouth.

Roots c. 1 mm diam., smooth, young tips green. Stems crowded, simple, erect, c. 46 cm tall, 4 6 mm diam. across the leaf-sheaths. Leaves adaxially deep green or purplish green, abaxially purplish, (narrowly) ovate-lanceolate, 6.0– 10.0 × 0.8–2.0 cm, apex unequally obtusely bilobed; leaf sheath tubular, 1.5 2.2 cm long, coarsely irregularly warty, along the mouth with a broad, oblique, ring-like swelling, opposite the leaf with a short, triangular lobe. Inflorescences breaking through the leaf-sheath opposite to and just below the nearest leaf, 2-flowered, the peduncle covered by a pair of persistent, obtuse scales forming a spathe 7–10 mm long. Pedicel and ovary 9.1 mm long, clavate, 6-ribbed, triangular in cross-section. Flowers opening widely, those in a pair facing away from each other (i.e., with the back of their mentums adjacent), bright golden yellow, the lateral lobes of the lip with some reddish spotting along the basal margins; column creamy yellow, the margins, in front and on the column-foot golden yellow suffused with red-purple, margins of clinandrium with a red-purple blotch, anther creamy yellow, pollinia white; pedicel and ovary light yellowish green. Dorsal sepal narrowly triangular, 3.8 × 0.6 cm, glabrous, acuminate. Lateral sepals obliquely narrowly triangular, falcate, 3.4 × 0.9 cm, glabrous, acuminate; mentum at right angles to ovary, 0.6 cm long, open in front, apex retuse, in side view obtuse. Petals linearoblong, slightly falcate, 3.4 × 0.5 cm, apical margins incurved, apex acuminate. Lip trilobed; lateral lobes erect, free part obliquely triangular, falcate, 4.5 × 2.3 mm, acuminate; between the lateral lobes with a single, smooth, slightly undulating keel extending to just below the base of the midlobe, on either side of the keel and on the lateral lobes with flattened, hair-like projections, some of which are connate at the base and form lamellae , free parts of the lateral lobes glabrous; midlobe strongly recurved in natural position, when flattened in outline broadly ovate-oblong, 10.7 × 7.5 mm, margins lacerate, apex forming an acute, triangular tooth, adaxial surface densely covered with numerous hair-like projections up to about 3 mm long, these are laterally flattened and in part have antler-like branching. Column 4.7 mm long, stigma longer than wide, subrectangular, margins of clinandrium denticulate; column foot 5.7 mm long, at right angles to the column, unadorned. Anther cap helmet-shaped, 1.8 mm long and wide, glabrous; pollinia 4, in 2 pairs, narrowly oblongoid, 1.7 mm long. Fruit not seen.

Habitat and Ecology: —Unknown.

Distribution: —Only known from Indonesian New Guinea.

Etymology:— From the Latin annulatus, ringed, referring to the ring-like swelling on the leaf sheaths.

Notes:— Plants of this relatively showy species were found in the orchid trade in Indonesia and were said to have been collected in Indonesian New Guinea. This seems credible, as all similar-looking species of D. sect. Grastidium are found there. The most striking feature of this species is the peculiarly warty and ringed leaf sheath. Some other species of Dendrobium have warty leaf sheaths, e g., D. gjellerupii as well as several species in D. sect. Calyptrochilus, but there the warts are finer, and the ring is absent. More similar in this respect is Glomera verrucifera Schlechter (1912: 286) , in which the leaf-sheaths are both strongly warty and provided with a ring-like swelling, much like D. annulatum . That at least two distantly related orchid species in the same area show such a striking similarity suggests that a similar selection pressure has been at work. In the case of Glomera and Dendrobium sect. Calyptrochilus , in which the flowers are probably bird-pollinated, we suggest that the rough (warty or papillose) leaf-sheaths help the birds to hold on to the stems while they probe the flowers. On the other hand, the flowers of D. annulatum , although brightly coloured, do not seem to have a morphology that points at bird-pollination. If our suggested function for the rough leaf sheaths is correct, then it could be that D. annulatum nonetheless is bird-pollinated. Additional support for this suggestion may be seen in the fact that the pollinia of D. annulatum are white, not bright yellow as is usually the case in orchids. Bird-pollinated orchids often have pollinia that are not brightly coloured, presumably to render them less conspicuous on bills. There may, of course, be an entirely different explanation for the surface texture of the leaf-sheaths in these orchids.

Discovery of this striking species confirms once more that the orchid flora of New Guinea is still far from completely known. It would be desirable to know the exact provenance of the new species described here, including its habitat, distribution, pollination ecology and population size. The uncontrolled trading in wild-collected orchid species in Indonesia needs to be taken seriously. Further research into the propagation and horticultural potential of this and related species is also recommended.

Figures

FIGURE 1. Dendrobium annulatum. A. Flowering plant. B. Habit. C. Stem. D. Detail of leaf-sheath with warts and ring. (Photos by Jeff Champion.)

FIGURE 2. Dendrobium annulatum. A. Flowers. B. Column, front view. C. Lip, basal view. D. Lip and column, side view. E. Column, side view. F. Lip, side view. G. Sepals and petals. H. Pollinia. (All photos by Jeff Champion.)

FIGURE 3. Dendrobium annulatum. A. Flowering plant. B. Leaf and leaf sheath. C. Stem with inflorescence. D. Flower. E. Dorsal sepal. F. Lateral sepal. G. Petal. H. Lip. J. Hairs on lip. K. Ovary, column and lip, lateral view. L. Column. M & N. Anther. O. Pollinia. A–C after photographs by Jeff Champion; D–O after spirit material of the isotype at K. Single scale bar 1 mm, double scale bar 1 cm (drawn by Judi Stone).