Phlegmariurus vanuatuensis A.R.Field, 2018
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publication ID |
https://dx.doi.org/10.3897/phytokeys.109.29359 |
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persistent identifier |
https://treatment.plazi.org/id/C0C7E47F-85A3-E81A-7610-D1C9B6C3264F |
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treatment provided by |
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scientific name |
Phlegmariurus vanuatuensis A.R.Field |
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sp. nov. |
Phlegmariurus vanuatuensis A.R.Field sp. nov. Figure 1 A–C View Figure 1 , Figure 2 D–F View Figure 2
Diagnosis.
Phlegmariurus vanuatuensis is similar to Phlegmariurus nummulariifolius but differs in having acutely spreading non-flattened sterile leaves (compared with adpressed and imbricate leaves flattened in on plane in P. nummulariifolius ), thicker pale green-brown stem bases 3.5-5.5 mm diameter in P. vanuatuensis (compared to thinner dark black-brown stem bases 1.5-3.5 mm diameter in P. nummulariifolius ) and a gradual transition to thicker less ramified fertile spikes 2-5.5 mm diameter in P. vanuatuensis (compared to an abrupt transition to slender ramified fertile spikes 1-2.5 mm in P. nummulariifolius ).
Type.
Nouvelle-Hebrides: Erromango, forêt dense au N du camp du km 17, alt. 300 m, 4 Aug 1971, J. Raynal RSNH 16213 (Holotype: P01221002!; isotype: P01219313!).
Description.
Sporophytes herbaceous, epiphytic, with tufted isodichotomous arching to pendulous shoots and with dichotomous roots emerging from the base of the tuft. Shoots abruptly to gradually heterophyllous; sterile sections leafy, 12-18 mm in diameter and usually 20-50 cm long, evenly branched 1-4 times; fertile sections filiform-funiform, 2-4.5 mm in diameter and up to 300 mm long, branched 0-3 times, usually unbranched at base. Stems fleshy, 2.5-5.5 mm in diameter in basal module without the leaves, pale green or light stramineous brown, and bearing indistinct longitudinal grooves between the rows of leaves. Leaves sessile, supine, decurrent, firm, orthostichous in four strict rows comprised of 2 alternating sub whorls of 2, acutely spreading, ovate to ovate-oval, 6-14.5 mm long × 6-9 mm wide, with a broad rounded base and rounded, obtusely pointed or acutely pointed apex, leaves flat to twisted with entire margins, mid glossy green to light yellow green. Leaves in the basal modules more crowded, ovate with an acute apex and with a narrowed sub-petiolate base, in median modules more widely spaced and diverging, sessile with an almost amplexicaule base, and in the distal modules transitioning in shape to sporophylls. Sporophylls gradually to sharply differentiated from sterile leaves, sessile, supine, orthostichous in two alternating pairs of two, acutely divergent to adpressed, scale like, ovate-rhomboid with a cuneate to rounded amplexicaule base and an acute apex, 1.5-5.2 mm long × 1.5-2.8 mm wide, overlapping. Sporangia borne on the upper surface in the axils of sporangia, reniform, 1-1.2 mm in diameter, mostly covered by the sporophyll. Spores isotetrahedral, 30-40 μm in diameter, with convex lateral margins, smooth proximal surfaces and moderately foveolate distal surface. Gametophytes holomycoheterotrophic, dorsiventral with paraphyses among the gametangia on the upper surface. Vanuatu flat tassel-fern.
Additional specimens examined.
VANUATU: Nouvelles Hebrides, [n.d.], M. MacDonald 59 (P01219315). Ile de Pentecôte, zone axiale: Lalak (cote 520), 15 Sep 1936, E. Aubert de la Rüe s.n. (P01219311). Vate, 500-600 m, May 1965, M. Schmid 188 (P01222833). Iles Banks, Vanua-Lava, epiphyte en forêt, 600 m, 14 Jun 1983, P. Morat 7472 (P01238484). NW of Efate, unnamed hill N of Trig Point above Narabut camp, occasional epiphyte in forest on summit of hill, 1600 ft [488 m], 5 Jul 1971, A.F. Braithwaite RSNH 2040 (P01219314). S. Erromanga, high epiphyte in forest, 300 ft [91 m], 6 Aug 1971, A.F. Braithwaite RSNH 2275 (P01219309). N. Espiritu Santo, Apouna Valley, epiphytic in forest, 3000 ft [914 m], 1 Sep 1971, A.F. Braithwaite RSNH 2355A (P01219310). N. Espiritu Santo S.W. Bay, occasional epiphyte in ridge top forest, 1300 ft [396 m], 11 Oct 1971, A.F. Braithwaite RSNH 2601 (P01219312). N. Espiritu Santo S.W. Bay, occasional epiphyte in ridge top forest, 1300 ft [396 m], 11 Oct 1971, J. Raynal RSNH 16213 (P01221002). Erromango epiphyte 300 m, 4 Aug 1971, J. Raynal RSNH 16213 (P01219313). Iles Banks, Vanua-Lava, crête vers, 500 m, 13 Jun 1983, J.M. Veillon 5542 (P01253017). Pentecôte, Enkul, 550 m, 28 Sep 1984, P. Cabalion 2568 (P01236864). Mallicolo, SW Bay, entre Lenbongbong et Lendemboi, 25 Sep 1986, G. Vourdy 823 (P01238278). Efate, M.A. Clements 5640 (CBG8916282). Cultivated James Cook University ex Efate, 30 Aug 2006, A.R. Field 1140 (BRI, CNS).
Distribution, habitat and ecology.
Endemic to Vanuatu where it occurs as an uncommon epiphyte on the bark of tree trunks and branches in the canopy to subcanopy of mature trees in lowland to montane primary tropical rainforest.
Conservation status.
Vulnerable. Phlegmariurus vanuatuensis is considered eligible for IUCN listing as Vulnerable ( IUCN 2012) on the basis of its Area of Occupancy being less than 20,000 km2. Its EOO was calculated at EOO 34,668 km2 and the AOO at 800 km2 using the GeoCAT tool. In addition, it meets criteria A.1.c. as it has experienced a catastrophic reduction in numbers and in particular loss of its intact rainforest canopy habitat following Tropical Cyclone Pam in 2015. It is also considered eligible for listing as Vulnerable on the basis of criteria B.1.a. as it has severely fragmented population scattered over disjunct islands, and is estimated to occur at fewer than 10 locations. In addition, it meets criterion B.1.b. (v & iv) as it is inferred to have experienced, and continue to experience an ongoing decline in the extent and quality of habitat and number of locations or subpopulations and number of mature individuals owing to land clearing of its habitat, and in particular owing to destruction of its habitat by severe tropical cyclones. In addition, the uniqueness of this species may make it a target for rare plant collectors.
Etymology.
Named for the origin of this species in Vanuatu. Vanuatu is a composition of the Austronesian words ‘Vanua’ ' meaning home or land and ‘Tu’ ' meaning stand.
Note.
Phlegmariurus vanuatuensis is closely related to P. nummulariifolius and has been hitherto included in that species. It appears to be the easternmost allopatric species of the P. nummulariifolius group, differing in several stable morphological characters. Living plants of both species are more distinct than pressed material (Figure 2 View Figure 2 ), as the characteristic divergent layered leaf architecture of P. vanuatuensis is flattened during pressing, the thick fleshy stems collapse and colour is lost during drying (Figure 2 View Figure 2 ). The lower stems of P. vanuatuensis are thicker, fleshier and light green or pale stramineous brown compared to P. nummulariifolius which has stems that are more slender, dark purplish brown and more lignified. The sterile leaves of P. vanuatuensis are acutely spreading, twisting slightly and being almost amplexicaule at their base compared with the tightly adpressed and uniformly planar flat leaves of P. nummulariifolius . The leaf colour of P. vanuatuensis is usually a bright green whereas in P. nummulariifolius it is usually a dark green. The fertile spikes of P. vanuatuensis are funiform and relatively unbranched compared with being filiform and multibranched in P. nummulariifolius . The transition from sterile to fertile spikes is more gradual than for P. nummulariifolius . Young plants of both species are very similar but can usually be differentiated on the basis of leaf divergence.
The diagnostic traits of Phlegmariurus vanuatuensis appear to be consistent across its population whereas the traits of Phlegmariurus nummulariifolius appear to be consistent throughout its Malesian, New Guinean and Solomon Island range with plants as close as the Santa Cruz Islands typical of P. nummulariifolius . It is expected that P. vanuatuensis has dispersed eastward from P. nummulariifolius , or a shared ancestor, but has become isolated in the islands Vanuatu leading to allopatric divergence there. Alternatively, it could have colonized Vanuatu and hybridized with P. phlegmarioides , as it also shares some traits with that species such as the divergent leaf planes, layered arching branches and the thicker stems and fertile spikes.
Phlegmariurus vanuatuensis can be readily differentiated from P. delbrueckii (Herter) A.R.Field & Bostock by its larger size, and by having terete fertile spikes rather than the quadrangular fertile spikes found in P. delbrueckii . It can be readily distinguished from P. phlegmarioides by its leaves being supine and somewhat more flattened in one plane, rather than radiating in four planar ranks as found in P. phlegmarioides . Another species occurring further east in Polynesia, P. ribourtii (Herter) A.R.Field & Bostock has thicker and distinctly quadrangular fertile spikes and more lingulate-oval leaves with a different arrangement.
Phlegmariurus vanuatuensis is remarkably convergent with the unrelated broad leafed form of P. obtusifolius (P.Beav.) A.R.Field & Bostock s.l. [= P. pachyphyllus (Kuhn ex Herter) A.R.Field & Testo s.s.] which occurs in a similar habitat in Madagascar and islands of the West Indian Ocean. Together, these species repeat a general trend in which several unrelated species of Phlegmariurus occurring epiphytically in lower altitudes of offshore oceanic islands have broader leaves with rounded apices.
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