Plagiothecium semimortuum var. semimortuum G.J.Wolski, 2024

Wolski, Grzegorz J., Latoszewski, Mikolaj, Cargill, D. Christine & Buck, William R., 2024, Re-assessment of type material of Plagiothecium novae-seelandiae Broth. and descriptions of four new Plagiothecium taxa (Bryophyta, Plagiotheciaceae) from Australasia, PhytoKeys 238, pp. 95-117 : 95

Plagiothecium semimortuum var. semimortuum G.J.Wolski sp. nov.

Type.

Holotype: Australia, Victoria, Mt. Stirling at the head of the Delatite River , along steep eastern face, 37°07'S, 146°28'E, alt. 5400 ft., growing on granite rock ledges and crevices along steep eastern face, growing together with Andreaea australis , leg. J. H. Williams 229W, 8 Mar. 1953 (MEL1016042!). Isotype: (WELT-M28128!) .

Description.

Plants medium size, ascending and julaceous, yellow-green to dark-green, with metallic luster, forming dense mats; stems 1.0-1.5 cm long, in cross-section rounded, with a diameter of 220-250 μm, the central strand well-developed, epidermal cells thick-walled, 10-15 × 10-12.5 μm, the parenchyma thin-walled, 9.0-14 × 8.0-13 μm; leaves symmetrical, ovate, folded, imbricate, closely arranged on the stem, concave, therefore leaves splitting when flattened, leaves from 1/3 up to 2/3 without protoplasts, those leaves from the middle of the stem 1.6-2.0 mm long and the width measured at the widest point 0.9-1.2 mm; the apex acute, not denticulate; costae two, rather thick and strong, extending usually to ½ of the leaf length, 250-300 μm; laminal cells more or less symmetrical, the length and width variable but dependent on location: 65.0-85 × 10-12.5 μm at apex, 60-90 × 10-12 μm at midleaf, and 65-100 × 15-17.5 μm toward insertion, due to the wide cells, cell areolation loose; decurrency of 4-5 rows of rounded and inflated cells, forming distinct auricles, 250-300 μm long (Fig. 8 ); sporophytes (immature) with setae reddish at base and yellowish-orange above, 1.5-1.8 cm long; the capsules inclined, 2.0 mm long, operculum long, conical and mammillate; sexual condition unknown.

Plagiothecium semimortuum var. semimortuum so far has been recorded from Australia, near Melbourne (MEL1031370, MEL1016042, CBG50739), Tasmania (HO302794, HO556631, HO133456) and from New Zealand (CHR651872, CHR532442, CHR464681, CHR104940). Specimens of P. semimortuum var. semimortuum were noted on the ground between plants (CHR651872); on humus between boulders (CHR532442); on shaded rock in exposed southerly sub-alpine herbfields with small scattered low shrubs (CBG50739); within rainforest gully (HO133456); on granite rock ledges and crevices along steep eastern face (MEL1016042, MEL1031370); on alpine heathland (HO556631); crevices in boulder fields (CHR104940); on mat of senescent tussock on vertical side of small valley, Chionochloa pallens - Chionochloa australis tussockland with scattered shrubs (CHR 464681). All specimens of P. semimortuum var. semimortuum have been collected in mountainous areas of Australasia (820-1769 m alt).

Etymology.

The name of this species - Plagiothecium semimortuum (Latin: semi - half; mortum - dead) refers to the leaves without protoplasts; they are dead even up to half the leaf.

Figures

Figure 8. Selected taxonomic features of Plagiothecium semimortuum var. semimortuum A, B shape and dimensions of leaves C decurrency on the stem D dimensions and shape of cells from middle part of the leaf (from the type of material of Plagiothecium semimortuum var. semimortuum MEL 1016042 and WELT-M 28128, photo. G. J. Wolski, November 13, 2022).