Marchesinia principensis Frank Müll. et Shevock, 2018

Müller, Frank & Shevock, James R., 2018, Marchesinia principensis (Marchantiophyta, Lejeuneaceae), a new liverwort species from Príncipe, West Africa, Phytotaxa 338 (2), pp. 202-208 : 203-206

Marchesinia principensis Frank Müll. et Shevock sp. nov. Figs. 1–3

Type: — SÃO TOMÉ AND PRÍNCIPE. Príncipe Island, Obô Natural Park de Príncipe. Along trail to Pico Papagaio above roça Santa Trindade, summit ridge of peak, 690 m, mixed hardwood tropical forest with ferns, on hardwood trunk in filtered light, 01°36’38.8”N, 07°23’32.0”E, 24 April 2012, Shevock 40193 (holotype DR, isotypes CAS, EGR, HSNU, STPH).

Diagnosis: Marchesinia principensis is similar to Marchesinia excavata , but differs in the broad reniform underleaves, 5–6 × as wide as the stem,>2 × as wide as long; the narrow angle that the ventral margin of the lobe makes with the keel (<90°), and the usually flat ventral margin of the lobe. Furthermore M. principensis is more robust than M. excavata (lobe length 1.0– 1.2 mm, lobe width 0.7–0.9 mm, leaf lobule length 280–350 μm, leaf lobule width 250–300 μm, underleaf width 1–1.3 mm).

Description: Shoots brown, to 8 cm long and 1.0– 2.2 mm wide, often forming extensive sheets. Stems 210–270 μm in diameter, with 22–24 cortical cells of brown colour and with equally strongly thickened walls, inner cells in 7–8 rows, lighter in colour, cells with very well developed radiate trigones; ventral merophyte 6–8 cell rows wide.

Leaves imbricate; lobes oval, 1.0– 1.2 mm long, 0.7–0.9 mm wide, convex, the apex rounded, but usually with 1–3 apical teeth, teeth 1–3 cells long, ventral margin arched, flat, and forming a well marked narrow angle (<90°, range 70–83°) with the keel. Cells in basal area elongate, 29–45 × 20–26 μm, cells in mid-lobe ± isodiametric, c. 18–30 μm, all cells with very well developed radiate trigones (edge length c. 7–10 μm) and intermediate thickenings; oil bodies not observed. Leaf lobules, when well developed, 0.2–0.35 times the length of the lobe, nearly flat, with a single, short 1–2-celled tooth, length of the lobules 280–350 μm, width 250–300 μm, cells smaller than lobe cells, + isodiametric, 11–16 μm.

Underleaves reniform, 5–6 × as wide as the stem, imbricate, recurved around the apex,>2 × as wide as long, width 1–1.3 mm, length 0.45–0.5 mm, the insertion line deeply arched, cells at insertion line brown, forming a small differentiated group, cells in the mid and upper part + isodiametric, 17–26 μm, basal cells elongated 27–36 × 18–22 μm, all with well-developed radiate trigones and intermediate thickenings.

Dioicous. Androecia intercalary on secondary shoots, bracts in 4–9 pairs. Gynoecia almost always with 2 equally long innovations, with the perianths lying in the bifurcations; bracts oval, 1.0– 1.5 mm long, 0.9–1.2 mm wide, convex, the apex rounded, but usually with 1–3 apical teeth, ventral margin arched, flat, and forming a wide angle with the keel (125–145°); bracteoles obovate, 1.2 mm long, 1.0– 1.1 mm wide, about as long as the bracts, apex rounded, apically with a few (1–4) distant teeth; perianths 1.3–1.8 mm long × 0.9–1.1 mm wide, oblong-obovate, plane or concave above, keeled laterally but not winged, moderately convex ventrally; rostrum very short, ca. 30 μm.

Etymology: The new species is named after the island on which it occurs.

Habitat and distribution: The species is known from only a few sites on Príncipe, at elevations of 500– 690 m. It grows on hardwood trunks and branches as well as on volcanic boulders in filtered light in mixed hardwood tropical forests.

Additional material seen (paratypes): SÃO TOMÉ AND PRÍNCIPE. Príncipe Island, Obô Natural Park de Príncipe: along trail to Pico Papagaio above roça Santa Trindade along ridge section of trail above the rope area, 550 m, mixed hardwood tropical forest, on volcanic boulders in filtered light, 01°36’45.0”N, 07°23’28.4”E, 24 April 2012, Shevock 40196 (DR, CAS, EGR, HSNU), on trail about the summit plateau of Pico Mesa accessed via the abandoned roça of Maria Correia, 500 m, mixed hardwood tropical forest with abundant bryophyte cover, on hardwood branch in filtered light, 01°34’55.5”N, 07°21’34.7”E, 28 April 2012, Shevock 40260 (DR, CAS, EGR, BOL, LISU, HSNU), along trail on rim of the Mesa in watershed of Ribeira Macoia above the old roça of Maria Correia, 01°34’53.4”N, 07°21’15.0”E, elev: 500 m, 23 April 2013, Shevock 42152A (CAS, DR, EGR).

Figures

FIGURE 1. Marchesinia principensis. A. Shoots in dry condition. B. Shoots in wet condition, ventral view. C. Stem in dorsal view. D. Stem in ventral view. All from Shevock 40260. Photos by F. Müller.

FIGURE 2. Marchesinia principensis. A. Lobes.B. Lobules.C. Underleaves.D. Stem cross section. E. Basal lobe cells. F. Mid-lobe cells. G. Cells at lobe apex. H. Stem in ventral view, underleaves are detached.All from Shevock 40260. Photos by F. Müller.

FIGURE 3. Marchesinia principensis. A. Stem with perianths and innovations in dorsal (left) and ventral (right) view. B. Perianth in dorsal view. C. Perianth apex. D. Bracteole. E. Bract. F. Cells in middle part of perianth. G. Secondary shoot with androecia. H. Male bracts.All from Shevock 40193. Photos by F. Müller.