Ptisana decipiens Murdock & C.W. Chen, 2020

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 decipiens Murdock & C.W. Chen sp. nov. Figures 4A-D , 6B, G

Type.

Solomon Islands. Guadalcanal: Logging site near Bomb Load Village, 300-400 m, 16 Aug 2012, C.-W. Chen & T.-C Hsu SITW00130. Holotype: BSIP. Isotypes TAIF [417070, 417072], TNM.

Diagnosis.

Differs from Ptisana ternatea (de Vriese) Murdock in having glabrous receptacles, synangia that do not extend to the apex of segments, pinnules gradually reducing in size toward the base of pinnae, and pinnule apices not abruptly acuminate. Differs from Ptisana melanesica (Kuhn) Murdock in having larger pinnules with submarginal synangia and smaller marginal teeth. The marked variability in size of ultimate segments has not been recorded in any other Ptisana species.

Description.

Ptisana decipiens var. decipiens : Fronds 3-pinnate, up to 2.5 m long. Stipe up to 1.2 m long, round in cross-section, surface green to brown, darkening with age, with reddish-blackish scales, the broader scales being darker in color, lenticels raised (Fig. 4B ). Fronds bearing 3 pairs of similarly sized pinnae on mature fronds, the terminal pair forking dichotomously at the frond apex, each pinna up to 1 m long. Swollen pulvini present at the base of all segments, green, smooth. Ultimate segments 5-12 pairs per pinnule, alternating on the costulae, largest at apex of each pinnule, smaller at the base, ultimate segments 9-18 cm long × 1.5-2.5 cm wide, elliptic to oblong with an acuminate apex; pinnule costulae gently zigzagging and clearly winged between segments (Figs 4A , 6G ). Laminae herbaceous-coriaceous, dark green above, pale below, with sparse brown-orange scales along the veins and midrib abaxially. Veins free, ca. 1.3 mm apart, rarely dividing once near the midrib (Fig. 6B ). Leaf margin gently serrate, more conspicuous at apex. Synangia green when immature, brown after opening, one per vein, submarginal, set back from leaf margin by 1-2 mm, ca. 1.8 mm long × 0.8 mm wide, 14-20 locules per synangium (Fig. 4C ), receptacles glabrous.

Etymology.

The epithet Ptisana decipiens (deceiving or misleading) refers to the morphological variation that has misled people into thinking two species were present.

Selected specimens examined.

Solomon Islands. Choiseul: Sirebe, 128 m, 4 Aug 2014, C.-W. Chen, W.-S. Wu & M. Fanerii SITW05882 (BSIP, TAIF [474134], TNM); Ranongga: Qiloe, 400-700 m, 16 Aug 2013, C.-W. Chen, T.-C. Hsu & M. Fanerii, SITW03102 (BSIP, TAIF [448596], TNM); Guadalcanal: Vunga Tubu, 100-500 m, 27 Jul 2014, C.-W. Chen, T.-C. Hsu & M. Fanerii, SITW05767 (BSIP, TAIF [472271], TNM); Malaita: Mt. Saranifilu, 700-800 m, 30 Jan 2015, H.-C. Hung, C.-W. Chen & M. Fanerii SITW08836 (BSIP, TAIF[501947], TNM); Makira: Materato to Mt. Gasi, 910 m, 1 Jul 2015, H.-C. Hung, C.-W. Chen & M. Fanerii SITW06724 (BSIP, TAIF [482700], TNM). Papua New Guinea. Manus Province: Los Negros, 17 Nov 1944, W.H. Wagner Jr. 3277bis (US [1860271]); New Ireland: Ambitle Island, 150 m, 7 Nov 2003, W. Takeuchi 16691 (US [3481228]).

Habitat and distribution.

Lowland forest, most commonly in gullies, also on hillsides below ridges. Commonly in association with Angiopteris microura Copel. Elevation range: 0-1550 m. Common. Solomon Islands (Baga, Choiseul, Guadalcanal, Santa Isabel, Makira, Malaita, Mono, New Georgia, Nggatokae, Nggela Sule, Ranongga, Rendova, San Jorge, Ulawa, Tetepare); Bougainville; New Ireland. A collection from Fergusson Island (10 Nov 76, J.R. Croft 68741, BISH, K, NSW [507470], US [3324251]) may also be this species.

Preliminary conservation assessment.

Both P. decipiens var. decipiens and P. decipiens var. delicata are widespread in the Solomon Islands and their habitat is not currently under significant threat. This species is currently considered Least Concern (LC) based on IUCN (2012).

Note.

There has been inconsistent use of the infraspecific ranks “subspecies” and “variety” through time, and even different preferences between pteridologists and other taxonomists ( Hamilton and Reichard 1992). We follow Yatskievych and Moran (1989), who recommend the use of subspecies in situations specifically involving geographically defined variation. Because of the overlapping ranges of the two taxa described here, and the presence of intermediate forms, which might indicate hybridization or ongoing diversification, we opted for the rank of variety in this case.

In most cases, the two varieties of P. decipiens are easy to distinguish based on segment size, but P. decipiens var. decipiens also has larger synangia with more locules. Occasional intermediates between the two varieties can be found, notably from Vella Lavella, New Georgia and Santa Isabel (Solomon Islands: Santa Isabel: D. Glenny 7211 (BSIP, W); Vella Lavella: 25 Oct 2013 C.W. Chen, T.-C. Hsu & M. Fanerii SITW05013 (TAIF [463907], TNM); New Georgia: 13 May 2013, Y.-H. Chang, W.-H. Wu, C.-F. Chen, C.-H. Hung & M. Fanerii SITW02317 (BSIP, TAIF [443219], TNM). The habitat of both varieties is the same, but the two varieties have not been observed together in any collection site. The range of the two varieties overlaps, but P. decipiens var. decipiens is more widespread, while P. decipiens var. delicata is more common in the Western Province.

The absence of indument on the receptacle is rare in Ptisana . This character was the basis for the obsolete genus Gymnotheca C.Presl, in which Presl included one species currently recognized in Ptisana , P. mertensiana (C.Presl) Murdock from the Caroline Islands.

Figures

Figure 4. Ptisana decipiens var. decipiens: A type specimen, with characteristically large segments B stipe showing scales C adaxial surface of fertile segments, showing vein spacing, synangial distance from margin, and winged costa. Ptisana decipiens var. delicata: D type specimen, with characteristically small segments E abaxial surface of fertile segment with maturing synangia. Photos: C. - W. Chen.

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.