Phlegmariurusvanuatuensis (Huperzioideae, Lycopodiaceae) a new species from Vanuatu, re-circumscription of P.nummulariifolius and new combinations in Phlegmariurus

Abstract Phlegmariurusvanuatuensis A.R.Field is described as a new species for plants endemic to the islands of Vanuatu that were previously identified with P.nummulariifolius (Blume) Ching. The Vanuatuan species differs from the widespread Asian-Oceanian species in several characteristics, most notably its acutely divergent leaf arrangement and thicker less branched fertile spikes. Phlegmariurusnummulariifolius is here re-circumscribed as plants occurring in Asia and into Oceania as far east as the Solomon Islands, being replaced eastwards by P.vanuatuensis. In addition, new nomenclatural combinations are made for Phlegmariurusaustralis, a species from Polynesia and for Phlegmariuruscopelandianus, a species from Malesia.


Introduction
Phlegmariurus Holub is a genus including epiphytic, epilithic and terrestrial plants that inhabit perhumid forests and montane regions throughout the tropics and subtropics globally. The global diversity of Phlegmariurus is grouped into a predominantly Neotropical clade which has dispersed several times into Africa, Madagascar and Hawaii and a predominantly Palaeotropical clade with a single dispersal into the Neotropics (Field et al. 2016;Bauret et al. 2018;Testo et al. 2018a, b). In Asia and Oceania, almost half the species diversity belong in as-yet unresolved clades related to P. phlegmaria (L.) Holub, P. phlegmarioides (Gaudich.) A.R. Field & Bostock and P. carinatus (Desv.) Ching or P. squarrosus (G.Forst.) Á.Löve & D.Löve and P. myrtifolius (G.Forst.) A.R. Field & Bostock (Field et al. 2016;Bauret et al. 2018;Testo et al. 2018a, b). Within Oceania, the diversity of Phlegmariurus has been taxonomically reviewed only in New Guinea, the Solomon Islands, New Caledonia, Fiji and Australia (Herter 1909;Herter 1916;Alderwerelt van Rosenburgh 1917;Compton 1922;Copeland 1929aCopeland , b, 1931Copeland , 1936Brownlie 1977;Jones and Gray 1985;Chinnock 1998;Field and Bostock 2008); but Vanuatu has been relatively neglected. Only one species, P. oceanianus (Herter) A.R.Field & Bostock has previously been described coming from Vanuatu, even though many other Vanuatuan specimens fit poorly into preexisting taxa from elsewhere. This paper examines the systematic placement of plants hitherto regarded as Phlegmariurus nummulariifolius (Blume) Ching occurring in Vanuatu and this species is herein described as new.

Methods
Herbarium materials of Phlegmariurus from across Asia and Oceania were examined in AAU, B, BONN-Nessel, BR, BRI, CANB, CNS, KLU, P, PR, PRC, QRS, UC and US. Living materials were examined both in the field in Australia and Asia as well as in cultivation at James Cook University, Australia. Measurements were taken both from herbarium specimens and living specimens, and where this differs it is noted. Herbarium acronyms follow Index Herbariorum [http://sweetgum.nybg.org/science/ih/] and standard forms of author and publication citations follow International Plant Name Index [https://www.ipni.org/]. Specimens annotated '!' have been physically seen, and specimens annotated '*' have been seen as photographs or scans.
A proposed Conservation status was assessed against the IUCN Red List Categories and Criteria (IUCN 2012). Area of Occupancy (AOO) and Extent of Occurrence (EOO) where calculated using the GeoCAT tool (http://geocat.kew.org/ Bachman et al. 2011) based upon map-assigned latitudes and longitudes extrapolated from herbarium labels and a grid cell of 10 km 2 . The centre of the island from which a specimen was selected in instances where no finer detail localities were recorded on herbarium labels.

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).
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.    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 km 2 . Its EOO was calculated at EOO 34,668 km 2 and the AOO at 800 km 2 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), 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). 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)  Description. Sporophytes herbaceous, epiphytic, with tufted isodichotomous pendulous shoots and with dichotomous roots emerging from the base of the tuft. Shoots abruptly heterophyllous; sterile sections leafy, 5-12 mm in diameter and usually 20-250 cm long, branched 1-6 times being relatively unbranched basally and more frequently ramified distally; fertile sections filiform, 1-2.2 mm in diameter and up to 400 mm long, multibranched 1-6 times. Stems slender and woody, 1.5-3.5 mm in diameter in basal module without the leaves, light green to dark purplish-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, adpressed and imbricate, ovate-oval, 6-14 mm long × 4-7.5 mm wide, with a rounded base and similar rounded apex, leaves flat with entire margins, dark glossy green to light yellow green. Basal leaves sometimes more scale like and leaves in basal modules sometimes lanceolate-ovate and more widely spaced out on elongated naked stems, leaves in median and distal regions ovate-oval. Sporophylls markedly differentiated from sterile leaves, sessile, supine, orthostichous in two alternating pairs of two, scale like, adpressed throughout, ovate-rhomboid with a cuneate base and acute apex, 2.1-3.5 mm long × 1.4-2.2 mm wide, overlapping or occasionally spaced apart with stem visible between subwhorls of sporophylls. Sporangia borne on the upper surface in the axils of sporangia, reniform, 0.  (Brownlie, 1977) are based on misidentifications of P. delbrueckii (Herter) Nessel (1939 p. 254). Schlechter's specimen is typical of P. nummulariifolius and it is presumed that he did not proceed with publication of a new taxon.

New combinations in Phlegmariurus
Recent combinations and descriptions of Phlegmariurus bring the number of combinations in the genus globally to 288 (Hsieh et al. 2012;Øllgaard 2012a, b;Field and Bostock 2013;Øllgaard 2015;Øllgaard 2016;Arana 2016;Field et al. 2016;Duy et al. 2016;Testo 2017;Kiew and Kamin 2018;Bauret et al. 2018;Øllgaard 2016). Although the Phlegmariurus species diversity of the Neotropics have been comprehensively reviewed by Øllgaard (1992, 2012a, b, 2015, 2016), the species occurring in the Palaeotropics have not been as intensively reviewed. Many Palaeotropical taxa are poorly defined, being either mixed assemblages of convergent species (e.g. species in the polyphyletic P. phlegmaria group, Field et al. 2016) or multiple taxa described for extremes of an apparently continuously variable species (e.g. species in the P. macgregorii group). The two following combinations are for more clearly definable species.