Distrianthes exxonmobilensis W.N.Takeuchi, 2015

Takeuchi, Wayne, 2015, Distrianthes exxonmobilensis (Loranthaceae), a new species in a formerly monotypic genus from Papua New Guinea, Phytotaxa 207 (2), pp. 200-204 : 200-203

Distrianthes exxonmobilensis W.N.Takeuchi , sp. nov. ( Figs. 1–3 )

Ab D. molliflorae (K.Schum.) Danser floribus 1 vel 3 (nec 6) differt.

Type: — PAPUA NEW GUINEA. Western Province: Juha South , mossy montane forest on limestone, 5°53.951’S, 142°26.037’E, 975 m, 18 February 2008, Takeuchi, Gambia & Jisaka 23094 (holotype A!; isotypes CANB!, LAE!) .

Stem-parasitic shrubs, glabrous. Branchlets compressed on new growth, cylindrical when older, 4–8 mm diameter at the top, nodose, straight, ascending; periderm crustaceous, pale brown (or fuliginous), lenticellate, not fissured; abscission scars crateriform, circular to rotund, 3.5–5 × 4–6 mm; internodes 4–11 cm long. Leaves opposite, exstipulate, lax, spreading; petioles 2–5 × 2–4 mm, articulate, planoconvex, transversely or reticulately wrinkled, usually concolorous with the attaching stem; leaf-blades lanceolate-ovate to elliptic, 6.2–12(–17.5) × 3.4–6.6 cm, often curved to one side, firm, thick, opaque, bifacially rugulose, adaxially sooty, abaxially orange brown to ferruginous; lamina base rounded (rarely cuneate), equal (or suboblique); margin undulate; apex attenuate, acute, or obtuse; venation brochidodromous and camptodromous, midrib slightly raised on both sides; secondaries 3–6, obscure, discolorous, filiform, near the lamina center with divergence angles of 25–60°, (10–)18–30(–42) mm apart, arcuate, closing by supramedially looping nerves or not, reticulum invisible. Inflorescence ramiflorous from branches 3–9 mm in diameter, rarely internodal; involucral bracts 2, lanceolate-ovate, 14–20 × 4–9 mm, opposed, acute, sessile, free (apparently never connate), involute, enveloping peduncles and flower bases, persisting, dark brown, papery. Flowers 6-merous, solitary or 3 together; peduncle columnar (a knobby callosity when older), 3–4 × 2.5–4(–6) mm, surfaces pale brown, flaky; pedicels absent—the flowers seated directly on peduncle summits; bracteoles 1, subtending calyces, deltate, 1–2 × 0.5– 1 mm, basally sheathing, caducous; calyx 2–3 × 2.2–2.5 mm, tube (ovary) obconical, distally flared, limb shallowly cupuliform, 0.8–1.2 mm long, margin hyaline, laciniate or lacerate; corolla sympetalous, in bud somewhat fusiform but with a conspicuously prolonged apex to 10 × 2 mm, inflated in the middle, longitudinally marked by 6 suture lines, membranous, reddish-brown, tube 32–45 × 0.8–2 × 4–6(–9) mm, straight (or curved), lobes valvate, attenuate, 12–16 × 1.5–2.5 mm, reflexed at anthesis; stamens epipetalous, inserted 7–8 mm from petal apices, erect, filaments strap-shaped, 3.5–4 × 0.4–0.5 mm, anthers linear, 4.5–5 mm long, introrse, apiculate; style sulcate, 55–60 × 0.2–0.3 mm, stigma capitate. Fruits unknown.

Etymology: —The new species is named after the Exxon Mobil tenements where many biological discoveries were made during the PNG LNG Pipeline surveys of 2008.

Field characters: —Stem-parasitic shrub; runners adhesively rooted to mossy tree trunks, vertically ascending, straight, branching at the top; leafy stems lax, spreading; blades inflexible, adaxially yellow green, abaxially whitishgreen; corolla red.

Distribution: —Known only from the type locality in the Strickland basin of Western Province, Papua New Guinea ( Fig. 4B ).

Habitat and ecology: —Mossy forest on limestone karst, sightings from 665–975 m (collection from 975 m).

Phenology: —Populations profusely flowering in February. Many fallen flowers on forest floors but no fruits seen.

Distrianthes Danser (1929: 312) is a genus previously recorded only from northern New Guinea, over an area between the Doorman River ( Fig. 4A ) in Indonesian Papua and Garaina ( Fig. 4C ) in Morobe Province ( Barlow 1981, 1997). As presently understood, Distrianthes is defined by the presence of 6-merous and sympetalous flowers in triads enclosed by involucral bracts (ibid.).

Three species have been historically published in Distrianthes : D. lamii (K. Krause 1924: 104) Danser (1929: 312) , D. molliflora (K. Krause 1922: 488) Danser (1929: 312) , and D. spathata (K. Krause 1922: 489) Danser (1929: 312) . Indument density, inflorescence dimensions, and connation of the involucral bracts are variable and intergrading among the described taxa. Owing to this character continuity, only D. molliflora is accepted by modern authorities ( Barlow 1981, 1997, Kuijt & Hansen 2015). While D. exxonmobilensis represents an extreme endpoint in the existing structural variation (e.g., glabrous flowers and free bracts), reduction of the inflorescence to a single flower or triad is a new generic quality whose significance is underscored by the geographic disjunction of its occurrence. Notwithstanding its novel features, D. exxonmobilensis is best accommodated within Distrianthes . Generic profiles based on single species will understandably prove too narrow if the genus is actually composed of more than one taxon.

The unusual involucre of D. exxonmobilensis can be compared to Papuanthes Danser (1931: 360) , a genus with reproductive structures similar to Distrianthes . However with pluriflorous heads (to 15 flowers together), and with bracts inserted at peduncle apices (vs. basal in Distrianthes ), any relationship to Papuanthes is more distant. Comparative morphology suggests Distrianthes is descended from Amyema stock ( Barlow 1997), but the presumed phylogeny is uncorroborated. Although DNA sequencing would be insightful, silica-dried samples have thus far been unavailable. The rarity of these plants ( D. molliflora was last seen ca. 30 years ago) has constrained application of modern techniques to their study.

With the species presented here, the generic range for Distrianthes is extended across the Central Divide and into the southern side of New Guinea. The geographic separation between Distrianthes and Papuanthes is decisively removed. Except for one locality in northern PNG, Papuanthes is historically known only from the southern provinces. All previous localities for Distrianthes were from areas north of the Dividing Ranges, on terranes comprising a distinct accretional phase from the tectonic paleohistory for D. exxonmobilensis (see Pigram & Davies 1987).

Figures

FIGURE 1. Distrianthes exxonmobilensis. Habit. A, detached inflorescence; B, unopened flowers on stem. A–B from Takeuchi, Gambia & Jisaka 23094.

FIGURE 2. Distrianthes exxonmobilensis. Vegetative structures. A, abaxial surfaces; B, adaxial surfaces. A–B from Takeuchi, Gambia & Jisaka 23094.

FIGURE 3. Distrianthes exxonmobilensis. Inflorescence. A, single flower subtended by two involucral bracts; B, immature triad; C, anthetic triad; D, flowering stem. A–D from Takeuchi, Gambia & Jisaka 23094.

FIGURE 4.IslandofNew Guinea.Localitiesfromthe text.A,DoormanRiver;B, JuhaSouth,type localityforDistrianthesexxonmobilensis; C, Garaina. Overlay (shaded area) shows distribution of the southern karst formations.