Radula smithii F.R.Oliveira-da-Silva, Ilk.-Borg. & Gradst

Oliveira-Da-Silva, Fúvio Rubens, Ilkiu-Borges, Anna Luiza & Gradstein, S. Robbert, 2022, Two new Neotropical taxa of Radula Dumort. (Marchantiophyta: Radulaceae) with bordered leaves, Phytotaxa 564 (1), pp. 95-103 : 99-100

Radula smithii F.R.Oliveira-da-Silva, Ilk.-Borg. & Gradst ., sp. nov. ( Fig. 4 , 5 , 2D–F )

Type:— PERU. San Martín: Rioja, Venceremos, km 390, Pedro Ruíz—Moyobamba road, primary montane forest, on soil bank, 05°50’S, 077°45’W, 1750–2100 m, 27 July–9 August 1983, D. N. Smith C-300 (holotype MO6968335 !, isotype MG!) .

Diagnosis:—Plants relatively robust, little branched. Leaf lobes distant, strongly convex, plane at the margin, the margin entire, bordered by 3-5 rows of thick-walled, reddish-brown cells. Lobules subquadrate with a rounded base covering 1/3(‒1/2) of the stem and distal margin usually recurved.

Description:—Dioicous? Plants relatively robust, ca. 4 cm long, (2‒) 2.5‒3 mm wide, yellowish-green to brown in herbarium, little branched, irregularly to dichotomous. Branches Radula - type, Lejeunea - type branches present on decapitated shoots. Stems 250‒350 µm diameter, in cross section with 45‒47 epidermal cells surrounding 98‒100 mostly larger medullary cells, epidermal wall heavily and evenly thickened, brownish, inner walls of the medullary cells thin-walled, yellowish. Leaf lobes obliquely to widely spreading, distant, rarely contiguous, strongly convex, suborbicular, 1.7‒2 mm long, 1.4‒1.5 mm wide, dorsal base straight, not covering the stem, apex rounded, margins plane, entire; marginal cells subquadrate to subrectangular or rounded, 10‒20 × 10‒15 µm, median cells isodiametric to elongate, 20‒25 × 15‒20 µm, basal cells elongate, 25‒35 × 15‒25 µm, cell walls thin at leaf base and in midleaf, evenly thickened and reddish-brown pigmented along the margin forming a broad, 3‒5 cell rows wide border, trigones absent, cuticle finely papillose. Lobules distant, subquadrate, 0.8‒1 mm long, 0.5‒0.6 mm wide, 1/4‒1/3 of lobe length, slightly inflated at the rhizoid area, insertion line almost straight, base plane, rounded, covering 1/3(‒1/2) of the stem, free margin plane, straight, apex plane, rounded, distal margin incurved, straight, keel slightly convex, angle with the stem 50‒60º, angle with the ventral margin of leaf lobe 150º‒160º. Rhizoids brown, scanty, on a few lobules. Sexual branches not observed. Vegetative reproduction by stem fragmentation.

Etymology:—The new species is dedicated to its collector, Dr. David Nelson Smith.

Distribution and habitat:—The new species is only known from northern Peru (Department of San Martín), growing on soil or as an epiphyte in primary montane forest at 1750-2100 m ( Fig. 3 ) together with Radula episcia Spruce (1885: 318) .

Taxonomic notes:— Radula smithii (subg. Volutoradula) is distinguished by the leaf lobes bordered by 3‒5 rows of thick-walled, reddish-brown cells, the border cells being strongly differentiated from those of the rest of the lobe. The border cells are distinctly pigmented and plane, while the rest of the leaf lobe cells are usually yellowish and strongly convex. The new species also stands out for the large, sparsely branched plants with very distant leaves.

Within Radula , a broad, pigmented leaf border of thick-walled cells otherwise occurs in R. ligula and R. marginata . The former species is widely distributed along the Atlantic coast of Brazil, with a single occurrence in Missiones, Argentina ( Reiner-Drehwald 1994, Oliveira-da-Silva et al. 2021), and is possibly a member of subg. Amentuloradula Devos et al. (2011: 1630); the latter species is endemic to New Zealand and belongs to the subgenus Amentuloradula ( Patiño et al. 2017). The border of R. ligula may be brownish in older leaves (Gradstein & Costa 2003) whereas that of R. marginata appears reddish in dorsal view ( Renner & Braggins 2004). Both species have ligulate lobules, parallel and close to the stem, being very different from those of the new species, which has subquadrate lobules. The stem anatomy of R. ligula and R. marginata is also different, with the outer epidermal walls being heavily and evenly thickened, more so than the inner epidermal walls (similar to R. pallens var. marginata ), while the inner epidermal cell wall and the medullary walls are thickened with concave trigones ( Oliveira-da-Silva et al. 2021 erroneously described the medulla in R. ligula as being “thin-walled”). In R. smithii , in contrast, the epidermal cell walls are thickened whereas the medullary cells are thin-walled, without any trigones.

Radula smithii is similar to members of the former sect. Dichotomae Grolle (1970: 666) (= subg. Volutoradula p.p.) in the shape and areolation of the leaf lobe, the lobule and its dichotomous branching pattern. The new species may be confused with two widely distributed Neotropical members of this group, R. pallens and R. episcia . In both collections of the new species, the plants were growing mixed with R. episcia , which was immediately separated from R. smithii by the absence of a leaf border and by the more imbricate leaves. The scarcity of dichotomous branching in R. smithii and R. episcia separates these two species from R. pallens , which produce copious dichotomous branching in female plants, due to paired innovations.

The montane forests along the Pedro Ruíz – Moyobamba road, where the new species was detected in 1983, had already been inventoried a year earlier by a team of bryologists in the framework of the BRYOTROP project (SchultzeMotel & Menzel 1987), and 17 species of Radula has been collected there, including the new species R. peruviana Yamada in Schultze-Motel & Menzel (1987: 79). Radula smithii , however, was not found during the BRYOTROP expedition and this suggests that the species may be a rare taxon as the plants are robust and unlikely to be overlooked in the field.

Additional specimen examined (paratype):— PERU. San Martín: Rioja, km 390, Pedro Ruíz – Moyobamba road, primary montane forest, epiphyte, 05°50’S, 077°45’W, 1750–2100 m, 27 July – 9 August 1983, D. N . Smith C-310 ( MO6869091 !, MG!) .

Figures

FIGURE 2. A–C. Radula pallens var. marginata. A. Habit, ventral view. B. Leaf lobe margin showing the border composed by thickwalled cells with large, bulging trigones. C. Cross section of stem. D–F. Radula smithii. D. Habit, ventral view. E. Leaf lobe margin showing the border composed of 3–4 rows of thick-walled, subquadrate to subrectangular or rounded cells. F. Cross section of stem (A, D= 1000µm; B–C= 50 µm; E= 200 µm; F= 100 µm; A–F from the holotype). Photograph taken by F. R. Oliveira-da-Silva.

FIGURE 3. Localization map of Radula pallens var. marginata (dot) and R. smithii (square). Map made by T. T. G. Takashima- Oliveira.

FIGURE 4. Radula smithii. A, I. Habit, ventral view. B, G. Cladographs of plants. C. Cross section of a leaf lobe, showing thick-walled, large, pigmented cells at leaf margin. D. Marginal leaf cells. E. Median leaf cells. F. Basal leaf cells. H. Leaves in dorsal view. J. Cross section of a stem (A, H, I= 1000 µm; C, J= 50 µm; D–F= 25 µm; A-J from the holotype). Drawing made by F. R. Oliveira-da-Silva and A. L. Ilkiu-Borges.

FIGURE 5. A–B. Scanning electron microscopy of the leaf lobe of Radula smithii, showing the difference between the border and the rest of the leaf lobe cells (A-B= 20 µm; A-B from the holotype). Photograph taken by H. T. Costi.