Stigmatodactylus aquamarinus, Robinson, Alastair S., Gironella, Elizabeth P. & Cervancia, Jehson M., 2016

Robinson, Alastair S., Gironella, Elizabeth P. & Cervancia, Jehson M., 2016, New orchid species of Sigmatodactylus (Orchidoideae; Diurideae) and a new record of Cryptostylis carinata from central Palawan, Philippines, Phytotaxa 252 (2), pp. 99-113 : 103-106

Stigmatodactylus aquamarinus A.S.Rob. & E.Gironella, sp. nov. ( Figs. 3 , 4 )

Type: — PHILIPPINES. Palawan: Mount Victoria Massif, 1460 m, in mossy pads on matted tree roots and steep rock walls, 25 Jul 2007, Robinson AR003 (holotype: PPC!; transfer to PNH requested) .

Stigmatodactylus aquamarinus is distinguished from S. lamrii ( Wood & Chan 1993: 274) by its labellum that is slightly oblong, retuse with an apiculate tip and an irregularly minutely serrulate margin, by its broader, unequal falcate petals, broader basal callus that is cuneate from above with two filiform protrusions at right angles to its axis and a glossy dark purple lingulate appendage that runs dorsally from the midpoint to the apex where its tip is slightly deflexed, and by its more obviously amplexicaul to perfoliate leaf.

Description: Terrestrial herbs, ca. 11.5–21.0 cm tall from apex of tuber to inflorescence apex. Tuber subglobose, ca. 4– 6 mm in diameter, pale brown, roots few, 0.4–2.5 cm long, emergent from tuber and below cataphyll. Stem erect, terete, green, glabrous, supple, 5.2–8.7 cm long, up to ca. 0.02 cm in diameter at the base, cataphyll 2–4 mm, enveloping base of stem. Leaf cordate, base auriculate to wholly perfoliate, ca. 1.1(–1.6) × 0.8(–1.2) cm, glabrous, green, margin sometimes minutely fimbriate. Inflorescence erect, terete, narrowing distally to ca. 0.45 mm, peduncle 6.5–12.5 cm, rachis 1.2–4.1 cm, green, with 1–3 flowers, usually 2, opening sequentially; floral bracts leaf-bearing, cordate, sessile to perfoliate, 3–5 × 2–4 mm, with an acuminate tip. Flowers facing outwards, resupinate, sepals and petals spreading widely, ca. 1.8–2.4(2.8) cm wide, translucent. Pedicel-ovary narrow, green, glabrous, 4–6 mm long, 0.4–0.7 mm in diameter, terete, longitudinally finely ribbed. Dorsal sepal erect to strongly arched backwards, linear-subulate and tubiform from involution of opposing margins, ca. 1.1–1.5 cm tall, 0.8 mm wide, slightly wider near the base where opposing margins are not involute. Lateral sepals small, ca. 5–7 mm long, linear-filiform, arched, descending to rear of labellum. Petals narrowly to broadly falcate, slightly unequal with a dorsal bias, flat, not horizontal, usually angled at 60–70º from vertical, ca. 0.9–1.5 cm long, conspicuously wide, up to 3.2 mm, but usually narrower. Labellum pale aquamarine to turquoise blue, usually with a faint, oblong flush of purple slightly above the centre, which in turn abruptly gives way to white towards the callus, petals and sepals more intensely coloured, proximally flushed purple around the midrib, column a darker bluish-green, basal part of keel usually purple, becoming green towards appendage, callus exterior pale blue, margins and filiform appendages more darkly so, callus dorsal appendage invariably deep purple. Labellum immobile, flat, shortly oblong-obovate, unlobed, up to 1.35 cm long, 1.1 cm wide, glabrous, margins minutely to obviously erose-serrulate, rarely scalloped, apex slightly retuse, in some blooms with an apiculate tip. Callus broad, porrect, 2.8–3.2 mm long, ca. 1.6–1.9 mm wide at base, cuneate, basally fused to column for ca. 1/5 its length, dorsal appendage running from midpoint to apex, glossy purple, lingulate, ovate-applanate, 0.35–0.55 mm wide, deflexed apex narrowly obtuse, callus lateral margins with pronounced filiform appendages at widest point, ca. 0.5 mm long, though highly inconsistent in terms of degree, the callus may be 3-lobed, the aliform lateral lobes being more or less appressed to the labellum and deeply cut, hyaline, to 0.8 mm long, if fully developed always terminating at boundary between white patch and oblong purple flush of colour on labellum. Column narrow, ca. 3–5.45 mm long, ca. 0.2–0.4 mm wide, straight for ca. 3/4 of its length, then variably decurved, basal 2/3 with a ventral keel, terminating in a large dactyliform appendage, 0.5–0.8 mm long, column apex clavate, rostellum unknown. Anther-cap bluish white, cucullate, broadly elliptic, notched. Anther bilocular, pollinia 4, waxy, ovoid, white (observed prior to maturation). Capsule narrowly ovate, 6–14 mm long, ca. 5–6 mm in diameter, 6-ribbed.

Conservation status: This species is known from three small populations of just 1–2 individuals each. Direct observations satisfy the IUCN Red List Criteria B2ac(iv);D ( IUCN, 2001) as CR (Critically Endangered). Despite numerous visits with successful sightings of its sister taxon, Stigmatodactylus dalagangpalawanicum , S. aquamarinus has not yet been observed at the same location more than once.

Distribution and Ecology: Growing terrestrially in moss pads overlying matted tree roots or steeply inclined ultramafic rock, generally occurring singly beneath closed canopy forest of upper montane trees 4–6 m tall or climbing bamboo; or in ultramafic rubble in open summit scrub, sheltered by large boulders. The known populations of Stigmatodactylus aquamarinus occur between 1430–1680 m.

Phenology: Plants and inflorescences bearing flowers observed in October, November and December, during the latter part of the wet season. Vegetative parts have been notably absent at other times of year, and the recurrence of plants at the same site in consecutive years has yet to be documented. This may suggest ephemeral colonisation of suitable sites, but data are too scant to be conclusive.

Etymology: The specific epithet, aquamarinus , is derived from the Latin aqua (water) and marinus (of the sea) = aquamarine, a reference to the unusual bluish to turquoise colour of the petals and sepals.

With the publication of Stigmatodactylus aquamarinus and S. dalagangpalawanicum , the total number of recognised Stigmatodactylus species now stands at thirteen. We place these in two groups that broadly reflect the species’ geographic ranges. The groups are summarised in Table 1.

Figures

FIGURE 3. Stigmatodactylus aquamarinus (from Robinson AR003 and living material studied in situ). A. Flowering plant; B. Flower from front; C. Flower from side; D. Labellum from front; E. Fruit; F. Oblique view of column; G. Petal; H. Dorsal sepal; I. Leaf. Drawing by A. S. Robinson.

FIGURE 4. Stigmatodactylus aquamarinus growing in situ in the Mount Victoria massif.