Didymoplexis stella-silvae Hermans, Kew Bull. 76: 46 (2021).
Description:
Erect holomycotrophic herb up to 9 cm tall, on a subterranean, stem-like rhizome, roots wiry, glabrous, c. 1.5 mm in diam. Rhizome terete, pale brown, elongate, a little verrucose, puberulent, ave. 12 x 0.3 cm. Leaves scale-like, at the base of the inflorescence, c. 5 x 3 mm. Inflorescence erect as an uninterrupted continuation of the rhizomatous stem, with 1 - 2 brown scarious scales towards the base. Peduncle slender, c. 1.5 mm in diam., with 2 - 3 short nodes, otherwise smooth, brown, bearing a short 3 mm scale below the rachis. Rachis apical, racemose with 1 - 4 flowers opening one at a time in succession. Floral bracts ovate, acute, 2 - 2.3 x 1.4 - 1.6 mm, verrucose abaxially. Flowers resupinate, spreading, reclining, overall 18 - 19 x 14x 16 mm, crystalline white except for the yellow-orange lip callus and base, the lip with a greenish-yellow triangle abaxially. Pedicel and ovary fusiform, 8 - 11 x 0.8 - 1.1 mm, with longitudinal ridges during flowering, minutely verrucose, pale brown. Dorsal sepal connate to the petals for 2 - 3 mm at the base, erect, broadly lanceolate, 8.1 - 8.5 x 4 - 4.3 mm, subacute, verrucose-warty on the exterior. Lateral sepals connate to each other at the base for c. 3 mm, spreading, ovate, 9.8 - 10.2 x 5 - 5.5 mm, obtuse to subacute. Petals oblanceolate, 6.9 - 7.2 x 3.8 - 4 mm, acute, partly adnate to the dorsal sepal. Lip with a strap-like 3 - 5 mm foot at the base, blade then reniform, truncate, margins curved, undulate, becoming serrate towards the anterior part, overall 5.1 - 5.3 x 9.1 - 9.3 mm, base claw-like, extended into a bilobed callus irregularly laciniate at the anterior margin, the blade with two irregular longitudinal rows of long thorn-like hairs, the entire lip mobile and seems to retract back against the column, during or after fertilisation. Column slender at the base, with short, triangular stelidia and with obovate, rounded arms just below the stelidia, 3.8 - 4 x 3.4 - 3.5 mm; anther elliptic, disk-like, c. 1.2 x 1.9 mm.
Etymology:
The name refers to the bright white flowers, resembling stars appearing on the forest floor.
Recognition:
Didymoplexis stella-silvae is a holomycotrophic plant with a thin erect inflorescence carrying few flowers opening successively and one at a time. The petals are adnate to the dorsal sepal and the lateral sepals adnate to one another. The mobile truncate reniform lip, undulate to laciniate at the margin, has two rows of thorn-like hairs, a bilobed callus becoming laciniate at the front, and a column with obovate, rounded arms just below the stelidia. The new species has some characteristics in common with a number of other Didymoplexis species but there are also several distinct differences. In the Africa - Madagascar region it has flowers about half the size of D. avaratraensis P.J.Cribb, Nusb. & L.Gaut. (Cribb et al. 2013: 43) and D. africana Summerh. (Summerhayes 1952: 465): the petals and sepals are also less fused, while the lip adornments and shape and callus are also very different. It has a similar habit and flower colour to D. verrucosa J.Stewart & Hennessy (1980: 841), but D. stella-silvae has 1 - 4 flowers (vs 8 - 12), the sepals and petals are connate (vs fused to the middle), the lip reniform (vs transversely triangular) and two rows of long hairs on the lip (vs lines of warts from base to tip). It is closest to Didymoplexis recurvata PJ.Cribb, Nusb. & L.Gaut. (Cribb et al. 2013: 44), recently described from northern Madagascar which is comparable in size and colour, the petals and sepals adnate toward their base, its lip shape and column wings being similar but D. stella-silvae has narrower petals, and the lip larger and broader (3.5 – 4 x 5 - 6 mm vs5.1 - 5.3 x 9.1 - 9.3 mm). Didymoplexis recurvata also lacks the rows of long hairs on the disk and has a 3-lobed callus at the base (vs 2-lobed).
Habitat:
Humid evergreen forest, in deep shade, in leaf litter and humus. Elevation 800 - 1070 m.
Flowering time:
December to January.
Notes:
Didymoplexis stella-silvae is another surprising discovery and brings the total to four, it is the first to be found in the central eastern forest of the island. The bright star-white flowers stand out in the deep shade of the forest; recently small colonies were observed and photographed in the Ranomafana National Park in a very well researched area near one of the main paths. It is likely that the species has rarely been seen because it has no leaves and the flowers only seem to open immediately after a significant rain shower and only remain open for less than a day, new flowers then open after the next rain shower. The pollination and lip mechanism deserves further research: the lip is hinged on a thin strap-like foot and was observed to retract against the column in a number of flowers, it is possible that the lip and its hairs act as a simple balance and flip back when visited by pollinators, it also possible that it just retracts after pollination has been effected or it may even be a trapping mechanism as has been observed in the South American orchid genus Porroglossum Schltr. (Schlechter 1920: 82).
Distribution:
Endemic to eastern Madagascar, Fianarantsoa province, around Ifanadiana and Ranomafana National Park.
References:
New species in Orchidaceae from Madagascar by Johan Hermans, Landy Rajaovelona & Phillip Cribb. KEW BULLETIN Published online: 15 March 2021.; POWO (2022). "Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; http://www.plantsoftheworldonline.org/ Retrieved 28 November 2022."
Images:
Click on each image to see a larger version.
Didymoplexis avaratraensis P.J.Cribb , Nusb. & L.Gaut. Candollea 68(1): 43. 2013 [12 Jul 2013]
Description:
Holomycotrophic herb up to 15 cm tall, stem beige, brown to blackish when old, growing from a subterranean elongated brownish tuberous rhizome. Leaves scale like, very small. Inflorescence erect, racemose, laxly few-flowered, the flowers opening one at a time and successively; peduncle slender, erect, bearing a small ovate bract below inflorescence, white or pale buff-coloured; rachis terete, slender; pedicel with longitudinal ridges 1.5-2 cm during flowering period; bracts ovate, acuminate, 1-1.5 mm long. Flowers with pink or white sepals and petals, flushed with red-brown in the centre, the lip pink or white with reddish brown sides, the callus spotted with yellow. Dorsal sepal strongly curved forward, lanceolate, rounded, 15 x 3.-3.5 mm; lateral sepals somewhat recurved, fused in basal half, more or less parallel and slightly falcate, ovate, rounded, 13 x 4 mm. Petals elliptic-lanceolate, acute, 13 x 4.5 mm, decurved at tip, adnate in basal fifth with sepals. Lip narrowly clawed at base, obovate-spatulate, truncate, 5-6 x 7-8 mm, the sides upcurved, bearing three patches on the apical lip lamina; callus at base shortly erect and bilobed at tip. Column 5-6 mm long, slender at base, with short recurved apical arms, triangular, broader than long and acute at the tips, G.7 mm long. Capsule unknown.
Etymology:
The specific epithet refers to the North ("Avaratra" in Malagasy) because the species occurs in the northern part of Madagascar.
Habitat and ecology:
Didymoplexis avaratraensis was recorded in evergreen forest on metamorphic rock; up to S2G m. This terrestrial herb occurs in forests with dense canopies reaching 1G to 15 m, with emergent trees reaching 1S to 2G m, with two woody strata in the canopy at 4 to 5 m and at 1 to 1.5 m high, and with an absent, sparse or very sparse ground flora, the soil densely covered with dry fallen leaves.
The most frequent species recorded together with D. avara-traensis (considering the Loky-Manambato population) in vegetation surveys include, in decreasing abundance : Croton sp., Dypsis nodifera Mart., Ravenea sambiranensis Jum. & H. Perrier, Dypsis aff. madagascariensis (Becc.) Beentje & J. Dransf. and Noronhia sp.
Flowering time:
November to December.
Notes:
Didymoplexis avaratraensis is clearly distinguished from the other African and Malagasy species of Didymoplexis known with flowers (Cribb, 1984; Cribb & al., 2G11) by its 2 lateral sepals fused to the mid-point while the remaining two petals and sepal are adnate together in the basal fifth, as well as by its column which has short recurved apical arms that are acute at the tips, and by its lip lacking rows of warts but with a bilobed callus at the apex. One observation of predation of flowering plants by some kind of invertebrate in one population is also interesting to note (Mark Clements, pers. comm.).
Distribution:
The species is known from Toamasina and Antsiranana provinces in North-East Madagascar. Four populations each of between (4)-15-2G individuals were observed, with a total of about 65-75 individuals observed in all sites.
Didymoplexis recurvata P.J.Cribb , Nusb. & L.Gaut. Candollea 68(1): 44. 2013 [12 Jul 2013]
Description:
Holomycotrophic herb up to 10 cm tall, growing from a subterranean elongated blackish tuberous rhizome. Leaves scale like, very small. Inflorescence erect, racemose, laxly up to 6-flowered, the flowers opening one at a time and successively; peduncle slender, erect, bearing a small ovate bract below inflorescence, white; rachis terete, slender; pedicel with longitudinal ridges; bracts ovate, acute, 1.5-2 mm long. Flowers with white sepals and petals and a white to rose-pink lip with a yellow callus, the column buff flushed. Dorsal sepal erect, lanceolate, subacute, 7-8 x 4-5 mm; lateral sepals adnate in basal third, ovate, rounded to subacute, 7-8 x 4-5 mm. Petals oblanceolate, acute, 7-8 x 5-7.5 mm, adnate in basal third to the sepals. Lip shortly narrowly clawed at base, very broadly obovate-spatulate, emarginate, 3.5-4 x 5-6 mm, slightly decurved at apex; callus on claw erect, dilated and 3-lobed at tip. Column 3.5-5 mm long, slender at base, strongly winged at apex, the wings dependent, recurved, rounded at tip, 1 mm long. Fruit unknown.
Etymology:
The specific epithet refers to the column with recurved apical arms bilobed at the tips.
Habitat and ecology:
Didymoplexis recurvata was recorded in evergreen montane forest on metamorphic rock; at 985 m. This terrestrial herb occurs in forests with canopies reaching 11 to 15 m, emergent trees reaching 21 to 24 m and with a second aborescent stratum at 8 to 10 m, with two woody strata at 5 to 7m and at 1 to 2 m high, and with a no herbaceous strata, the soil densely covered with dry leaves of trees. recurvata in Loky-Manambato vegetation surveys include, in decreasing abundance: Marojejya insignis Humbert, Ravenea sambiranensis Jum. & H. Perrier, Dypsis nodifera Mart., Wein-mannia decora Tul., Syzygium condensatum (Baker) Labat & G. E. Schatz, Plagioscyphus aff. louvelii Danguy & Choux and Blechnum attenuatum (Sw.) Mett. var. attenuatum.
Flowering time:
December.
Notes:
Didymoplexis recurvata is clearly distinguished from the other African and Malagasy species of Didymoplexis known in flower by its column which has short recurved apical arms that are bilobed at the tips, as well as by its lip which lacks rows of warts but has at the base a tall apically trilobed entire callus and by its sepals and petals that are adnate in the basal third.
Distribution:
The species is only known from the Binara forests in the Loky-Manambato (Daraina) region, in Antsiranana Province in North-East Madagascar. Only 1520 individuals were observed in one population in the Loky-Manambato region among the 54,000 plant occurrences recorded during the Loky-Manambato vegetation study.
Didymoplexis verrucosa J.Stewart & Hennessy, Amer. Orchid Soc. Bull. 49: 841 (1980).
Description:
Herb, holomycotrophic, glabrous, leafless. Tuber elongate, moniliform, branching, up to 90 mm long, 20 mm in diam. Scape erect, 10-15 cm tall, bearing two sheathing cataphylls at the base, 8- to 12-flowered; bracts spreading, ovate to triangular-ovate, 1-2 mm long. Flowers non-resupinate, white, 1013 mm across; pedicel and ovary 10-16 mm long; sepals and petals connate into a short tube at the base; dorsal sepal oblong, obtuse or rounded at the tip, 6-8 x 3-4 mm, connate for 1-2 mm with the petals; lateral sepal similar but connate for 1 mm or less to the dorsal sepal; petals oblong, obtuse or rounded, 5-6 x 2-4 mm; lip erect-spreading, free, shortly clawed, transversely triangular, 3-lobed at apex, 5-6 x 8-9 mm; callus of two lines of small warts from base to tip, with a fleshy yellow ligule on the claw; column straight, 4 mm long. Capsule narrowly ovoid-elliptic, 20 mm long, 10 mm in diam., pedicel extending erect to 100-200 mm as the capsule develops.
Habitat:
In coastal forest on sand in South Africa and in forest on tsingy (eroded limestone) in Madagascar; 0-100 m.
Distribution:
KwaZulu-Natal, W. Madagascar
Didymoplexis africana Summerh., Kew Bull. 6: 465 (1951 publ. 1952).
Description:
Leafless, glabrous saprophytic herb; tubers up to 4 × 0.7 cm, fusiform. Scape slender, 8–21 cm high. Stem with 2–3 sheathing cataphylls c. 2 mm long near base. Inflorescence densely 1 to many-flowered. Flowers spreading or erect, white or cream flushed with pink. Ovary and pedicel 10 mm long at anthesis. Tepals connate for about half their length forming a bilabiate tube. Dorsal sepal erect, 15 × 3.5–4 mm, subspathulate, joined to petals for c. 7.5 mm. Lateral sepals 10.5–12 × 3.25–3.5 mm, subspathulate, joined to each other for 7.5 mm and to petals for 4.5 mm. All sepals verrucose outside. Petals 10.5–12 × 3.5–4.5 mm. Lip free, 10–11 × 5.5 mm, clawed at base then flabellate-orbicular, erose-denticulate at margin with a transverse fleshy callus below apex and a reflexed, ligule-like callus at apex of claw. Column c. 10 mm long, straight, with tridentate apex. Anther hemispherical; pollinia 4, ovoid. Rostellum fleshy.
Habitat:
In deep shade in leaf litter of submontane evergreen forest up to c. 800 m.
Distribution:
W. Trop. Africa to Tanzania
