Radula longicarinata

Oliveira-Da-Silva, Fúvio R. & Gradstein, S. Robbert, 2024, High liverwort diversity in the tropical Andes as evidenced by the discovery of three new species of Radula (Radulaceae), Phytotaxa 653 (1), pp. 91-99 : 94-96

Radula longicarinata F.R.Oliveira-da-Silva, sp. nov. ( Fig. 3 )

Type:— BOLIVIA. La Paz: Franz Tamayo, Area Natural de Manejo Integrado Apolobamba, Queara , Supay Cocha , “fragmento relicto del bosque de yungas altoandino con Polylepis y Gynoxys , sobre roca en sombra”, 14°43’40” S, 69°04’16” W, 4040 m, 17 April 2008, A. Fuentes et al. 12708 (holotype, MO-6097704!, c. gyn.; isotype, MG!) .

Diagnosis:—Plants relatively robust, 2.5‒3 mm wide, regularly pinnate. Leaf lobes widely spreading, distant to contiguous, orbicular to falcate-ovate. Lobules distant, narrowly obtriangularly elongate, 0.7‒1.1 mm long, 0.4‒0.5 mm wide, flat, insertion 4‒6× the base length, insertion line straight, keel straight, spreading at a very narrow angle of 20‒30º with the stem.

Description:—Dioicous. Plants 2.5‒3 mm wide, to 2 cm long, green to yellowish-green in herbarium, regularly pinnate. Stems ca. 200 µm in diam., with thick-walled, brownish epidermal cells surrounding mostly larger, thin-walled, colorless medullary cells, outer epidermal wall heavily and evenly thickened, more so than the inner epidermal wall. Leaf lobes widely spreading, distant to contiguous, subimbricate on branches, plane, orbicular to falcate-ovate, 1.5‒1.8 mm long, 1.1‒1.4 mm wide, dorsal base rounded, overlapping the stem, dorsal margin rounded, ventral margin rounded, apex rounded to obtuse, margin plane, entire; marginal cells subquadrate to subrectangular, 10‒15 × 8‒10 µm, median cells isodiametric to elongate, 15‒20(‒22) × 12‒20 µm, basal cells isodiametric to elongate, 20‒25 × 15‒20 µm, cell walls thin, trigones small to lacking, intermediate thickening lacking, cuticle smooth; oil bodies not observed. Lobules distant, narrowly obtriangularly elongate, 0.7‒1.1 mm long, 0.4‒0.5 mm wide, ca. 1/3 the lobe length, flat, insertion 4‒6× the base length, insertion line straight, base plane, rounded, covering ca. 1/2 the stem, free margin plane, straight, apex plane, rounded to slightly obtuse, distal margin straight; keel straight, convex on lobules of the branches, spreading at very narrow angles of only 20‒30º with the stem and at 90‒110º with the ventral lobe margin, at its junction with the lobule. Rhizoids lacking. Androecia not observed. Gynoecia on long branches, with 2 innovations; bracts ovate, 0.9‒1.2 mm long, 0.6‒0.7 mm wide, apex rounded, margin plane to recurved, entire, lobule oblong, 1/3‒1/2 of lobe length, apex acute; mature perianth absent. Vegetative reproduction not observed.

Etymology: —The epithet “ longicarinata ” refers to the long keel of the lobule.

Distribution and habitat: —The new species is only known from the type locality in the province of Franz Tamayo ( Fig. 2 ), Department of La Paz, Bolivia. Radula longicarinata was found at 4040 m on shaded rock, in a subalpine forest stand dominated by dwarf tree species of Polylepis Ruiz & Pavón (1794: 80) and Gynoxys Cassini (1827: 455) .

Taxonomic notes: — Radula longicarinata is recognized by the regularly pinnate plants with distant to contiguous leaves, lobules narrowly obtriangularly elongate, 3–4× longer than wide and flat, insertion line straight, long, 4‒6× the base length, and keel long and straight, spreading at very narrow angles of only 20‒30º with the stem. Branches may have shorter, subquadrate to obconic lobules, which are strongly inflated along the keel or not and with a straight to concave keel.

The new species resembles Radula bischlerae from Colombia by the obtriangularly elongate lobule, which is much longer than wide; both species occur at high, alpine elevations in the tropical Andes. However, R. bischlerae is a very fragile plant with strongly caducous leaf lobes and tubularly inflated lobules with a curved insertion line. In R. longicarinata caducous leaves are lacking and the lobules are plane, with a straight line of insertion. In addition, R. bischlerae is smaller (1‒1.5[‒2] mm wide) than the new species (2.5‒3 mm wide).

Radula longicarinata is a distinct, new member of Radula subg. Volutoradula .

Figures

FIGURE 2. Distribution of Radula ilkiuborgesiae (green dot), R. longicarinata (red triangle) and R. magna (yellow pentagon). Map made by Paulo Eduardo Silva Bezerra.

FIGURE 3. Radula longicarinata. A. Marginal leaf cells. B. Median leaf cells. C. Basal leaf cells. D. Habit with gynoecia. E. Habit. F. Leaves. G. Cross section of stem. H. Cladographs of plants (U = gynoecia without perianth) (A-C, G = 50 µm, D-F = 500 µm; All from the holotype).