Ptisana smithii (Mett. ex Kuhn) Murdock, 2008

Murdock, Andrew G., Chen, Cheng-Wei, Huang, Yao-Moan & Glenny, David, 2020, Affinities of the fern genus Ptisana (Marattiaceae) in the Solomon Islands, with descriptions of two new species, PhytoKeys 170, pp. 1-23 : 1

Ptisana smithii (Mett. ex Kuhn) Murdock Figures 5B, D, F , 6E, J

Marattia smithii Mett. ex Kuhn, Verh. K.K. Zool.-Bot. Ges. Wien 19: 584. 1869 (lectotype, designated by Murdock 2008b, pg. 748: Aneiteum, New Hebrides, Dec 1858, Herus 5 (lectotype: P!; isolectotype: GH!).

Description.

Fronds 2-pinnate, up to 2.5 m long. Stipe up to 1.2 m long, 2-4 cm diameter at the base, circular in cross-section, surface dark brown to blackish-green, lighter around lenticels, with lacerate rusty scales mixed with broader brown-black scales, base of stipe bearing dense broad brown scales. Fronds bearing 5-8 pairs of pinnae, opposite to subopposite and well-spaced on the rachis, with a single terminal pinna or forking dichotomously at the frond apex, the proximal pinnae somewhat reduced in size (Fig. 5B ). Swollen pulvini present at the base of all segments, pulvini of primary division often with a dorsal ridge, smooth and with a lighter color on secondary divisions (Fig. 5F ). Ultimate segments 15-20 cm long × 2-2.5 cm wide, narrowly oblong, base rounded but asymmetric, more cuneate acroscopically, apex acuminate (Fig. 6J ). Laminae coriaceous, dark green above, pale below, with sparse tan scales along the veins and midrib abaxially. Leaf margin lightly serrate, often strongly repand. Veins simple, ca. 1.5 mm apart, rarely dividing once near the midrib, curving toward the apex on the marginal side of each synangium (Fig. 6E ). Synangia submarginal, 2.0 mm long × 0.8 mm wide, 16-20 locules per synangium (Fig. 5D ), receptacles bearing short hairs.

Selected specimens examined.

Solomon Islands. Vanikoro: Rain forest, 100 m, 1928, S.F. Kajewski 677 (F, UC [UC422670, UC1007994], MICH [1177187], US [1916159]); Ngarabu camp, 120-600 m, 17 Jun 2016, C.-W. Chen & T.-C. Hsu & M. Fanerii SITW10574 (BSIP, TAIF [498575, 520559], TNM); Airport to Uleule River, 20-250 m, 20 Jun 2016, C.-W. Chen & T.-C. Hsu & M. Fanerii SITW11037 (BSIP, TAIF [498870, 498871, 498872, 498873, 498874], TNM). Vanuatu. Aneityum: Southeast, 200 m, 26 Jul 1971, M. Schmid 3905 (L). Fiji. Rewa Province: Suva city, I-Suva Forest Park, 17 Sep 2013, C.-W. Chen Wade3093 (TAIF [439749, 439750, 439751, 439752]).

Habitat and distribution.

Lowland forest, growing along streams and steep hillsides. Solomon Islands: Vanikoro, likely to be found on Nendo; Vanuatu; Fiji; Tonga; Samoa.

Preliminary conservation assessment.

Ptisana smithii is only known from collections from Vanikoro in the Solomon Islands, but it is widespread in adjacent island groups. It is currently considered Least Concern (LC) based on IUCN (2012).

Note.

The Santa Cruz group is the northern limit of the range of this species. The Salicina clade (Fig. 2 ), which includes P. smithii , is in need of revision. There are clear sequence and morphological differences from archipelago to archipelago across the Pacific. The Fijian collection sequenced for this study had synangia that were more medial than those from the Solomon Islands. Brownlie (1977) described Fijian species as having alternate pinnae, but examination of collections and photographs shows that Fijian plants have opposite or subopposite pinnae as observed in the Solomon Islands. We are retaining the use of the name P. smithii here because the morphology agrees so closely with collections from Vanuatu, the type locality, and we anticipate that future work will likely split P. salicina into a number of geographically distinct taxa.

Figures

Figure 2. Phylogeny of Ptisana based on rps 4 - trnS and trnSGG plastid sequence data. Bayesian consensus tree, with branch support values (ML bootstrap support / Bayesian posterior probability); • = 100. The four species recognized in the Solomon Islands are marked by colored bars. Key clades discussed in text marked by arrows.

Figure 5. Comparison of Ptisana papuana (left column) and Ptisana smithii (right column) A, B whole plants Ptisana smithii B showing its distinctively repand margins C, D fertile segments with mature synangia. Ptisana papuana (left) has longer synangia that reach nearly the midpoint between the margin and the midrib, and conspicuously serrate margins E, F Pulvini, closeup.

Figure 6. Comparison of venation and margins (A-E) and apices of ultimate segments (F, G) of the Ptisana species in the Solomon Islands A, F P. ambulans B, G P. decipiens var. decipiens C, H P. decipiens var. delicata D, I P. papuana E, J P. smithii. Scale bars: 5 mm.