# Lempholemma polycarpum

Lempholemma polycarpum is a little-known species of saxicolous (rock-dwelling) lichen in the family Lichinaceae. It was first described from Yemen and is characterised by its blackish thallus, abundant small apothecia (fruiting bodies), and cyanobacteria from the genus Nostoc as its photobiont. The lichen is found on inclined limestone boulders in sun-exposed habitats with open forest vegetation. It also occurs in Madagascar and in Aldabra.

## Taxonomy

The lichen was first formally described by the German lichenologist Matthias Schultz. The type specimen of Lempholemma polycarpum was collected in Shah-ot, Damkaur, Al Mahrah Governorate, Yemen, on small inclined limestone boulders at an elevation of 680 m (2,230 ft). The species epithet polycarpum refers to the abundantly produced, small apothecia.

## Description

The thallus of Lempholemma polycarpum is blackish, dull, and rarely slightly pruinose, with a gelatinous texture when wet. Thalli consist of individual, regular, umbilicate-lobate rosettes measuring 3–6 mm in size. Lobes are radiating, free, tongue-shaped, and convex, with short lengths of 1.5–2.5 mm, widths of 0.5–0.6 mm, and thicknesses of 0.25–0.45 mm. The surface of the lobes is smooth but becomes verrucose when numerous small apothecia are produced.
Microscopically, the mycobiont forms a loose network of elongated hyphae that becomes denser towards the lobe margins, with cells measuring 10–17.5 by 1.5–2 (up to 5) μm. The photobiont is Nostoc, which forms twisted and bent, bead-like chains of 5–20 spherical to ellipsoid cells. Photobiont cells are 3–5 μm wide without the sheath, and 10–12.5 μm wide with the sheath. The gelatinous sheath is hyaline in the thallus centre and yellowish-brown towards the upper surface. Apothecia are usually abundant, with 1–10 per lobe, and are very small, measuring 200 (up to 250) μm wide. They are immersed to partially immersed in the thallus with a low thalline margin, and have a reddish-black apothecial disc when dry, which turns dark red when moist. Ascospores number eight per ascus, are simple, hyaline, and broadly ellipsoid, measuring 12.4–6.5 μm; their spore wall thickens with age, reaching up to 1.5 μm wide.

### Similar species

Lempholemma polycarpum is similar to Lempholemma socotranum, but the latter has an umbilicate-squamulose thallus with incised to short-lobed margins, larger apothecia with wider, open discs, and smaller ascospores. Lempholemma radiatum has elongated, radiating lobes that are longitudinally ridged and plicate, and it differs in the presence of isidia, the type of ascoma ontogeny, and a more or less arctic distribution. Lempholemma lingulatum is another lobate member of the genus, but its lobes are unbranched, distinctly tongue-shaped, and widened at the tips. Lempholemma polycarpum is also similar to Collema multipartitum and C. fragile, both of which occur in similar habitats on Socotra. The former species differs in the presence of eventually sessile apothecia, septate ascospores, amyloid ascus tips, and finely striate lobes, while the latter differs mainly in the presence of laminal isidia on more stunted, shortly forked lobes with usually pruinose tips.

## Habitat and distribution

Lempholemma polycarpum grows on inclined limestone boulders in sun-exposed habitats on rocky slopes with open forest vegetation. It is known from two localities in southeast Yemen. The species is found growing alongside Paulia aldabrensis, P. perforata, Lempholemma botryosum, and a species of Psorotichia. Three other species of Lempholemma are known to occur in the Arabian Peninsula and Socotra: Lempholemma socotranum, L. intricatum, and L. botryosum. Lempholemma polycarpum has also been recorded in Madagascar, and in Aldabra.