Radula ilkiuborgesiae

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 : 92

Radula ilkiuborgesiae F.R.Oliveira-da-Silva & Gradst., sp. nov. ( Fig. 1 )

Type:— COLOMBIA. Santander: Valle de San José , 3250 m, 11 September 1957, P. J. Grubb & D. A. Guymer B 446 B (holotype, BM-013763001!; isotype, MG!) .

Diagnosis:—Plants minute, 0.5‒0.7 mm wide, to 1 cm long. Leaf lobes obliquely to widely spreading, distant, convex, oblong-ovate. Lobules distant, subrectangular and very long, ca. 2/3 the lobe length, strongly inflated along the keel, insertion line curved, base not covering the stem, keel convex. Androecia terminal on long branches, with 15‒30 pairs of bracts.

Description:—Dioicous. Plants 0.5‒0.7 mm wide, to 1 cm long, yellowish to brownish in herbarium, regularly pinnate. Stems 80‒100 µm in diam., with thick-walled epidermal cells surrounding thin-walled and similar-sized medullary cells, outer epidermal wall heavily and evenly thickened, more so than the inner epidermal wall, the walls yellowish. Leaf lobes obliquely to widely spreading, distant, convex, oblong-ovate, 0.3‒0.5 mm long, 0.2‒0.3 mm wide, dorsal base rounded, covering up to 1/3 the stem, dorsal margin slightly rounded, ventral margin straight to slightly rounded, apex rounded, margin plane, entire; marginal cells subquadrate to subrectangular, 11‒18 × 7‒11 µm, median and basal cells isodiametric to elongated, 15‒22 × 8‒15 µm, cell walls thin, trigones small to lacking, intermediate thickening lacking, cuticle smooth; oil bodies 1 per cell, spherical to ellipsoidal, yellow, smooth, 8–16 × 8‒10 µm. Lobules distant, subrectangular, 0.25‒0.3 mm long, 0.1‒0.14 mm wide, ca. 2/3 of lobe length, strongly inflated along the keel, insertion line curved, base not covering the stem, free margin plane, straight to sinuose, apex plane, rounded to slightly obtuse, distal margin straight to sinuose; keel convex, spreading at angles of 35‒45º with the stem and at 160‒180º with the ventral lobe margin, at its junction with the lobule. Rhizoids colorless, long, scanty, present on a few lobules. Androecia terminal on long branches, with 15‒30 pairs of bracts, ca. 0.2 mm wide; bracts contiguous to imbricate, oblong-ovate, ca. 0.3 mm long, ca. 0.1 mm wide, apex rounded, margin plane, entire, lobule distant to contiguous, oblong-ovate, ca. 3/4 of lobe length, base straight, free margin straight, apex rounded. Gynoecia and vegetative reproduction not observed.

Etymology:—The new species is dedicated to Dr. Anna Luiza Ilkiu-Borges in recognition of her important contributions to bryology, especially the taxonomy of liverworts.

Distribution and habitat:—The new species is only known from the type locality in Valle de San José ( Fig. 2 ), Department of Santander, Colombia, where it was collected near the lower edge of the páramo at 3250 m elevation.

Taxonomic notes:— Radula ilkiuborgesiae is the smallest species among Neotropical Radula , with shoots 0.5‒0.7 mm wide and up to 1 cm long. The new species is readily distinguished by the usually widely spreading, oblong-ovate leaf lobes, the long subrectangular lobules, ca. 2/3 of lobe length and strongly inflated along the keel, and the very long male spikes, consisting of up to 30 pairs of bracts. The latter characteristic is unique among Neotropical Radula species which normally have androecia consisting of 1‒10(‒12) pairs of bracts, exceptionally to 20 pairs (seen in a few specimens of Radula javanica Gottsche [in Gottsche et al. 1845: 257]).

By its very small size Radula ilkiuborgesiae approaches R. brasilica K. Yamada (1993: 35) (plants 0.8‒1.4 mm wide), but the latter species differs in having a strongly recurved free margin of lobules and very fragile leaf lobes, often resulting in almost denuded branches. The diagnostic characters of Radula ilkiuborgesiae are unparalleled among the Radula species from tropical America. At a first glance, the new species resembles Cololejeunea ( Spruce 1884: 291) Stephani (1891: 202) ( Lejeuneaceae ), but in the latter genus rhizoids are produced on the stem (not on the lobule surface) and the stem epidermis cells are thin-walled. The thick-walled stem epidermis surrounding a thin-walled medulla places R. ilkiuborgesiae in R. subg. Volutoradula Devos et al. (2011: 1629). Nevertheless, by its yellowish epidermal wall this new species stands somewhat isolated among the members of the subgenus which normally have a brown epidermal wall.

Figures

FIGURE 1. Radula ilkiuborgesiae. A. Habit with androecia. B. Marginal leaf cells. C. Habit. D. Median leaf cell with oil bodies. E. Median leaf cells. F. Cladograph of plants. G. Habit. H. Leaves. I. Cross section of stem. J. Habit in dorsal view (A, C, G = 500 µm, B, D, E = 25 µm, H = 100 µm, I = 50 µm, J = 250 µm; All from the holotype).

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