Dictyonema krogiae is a species of basidiolichen in the family Hygrophoraceae. It is found in Kenya, where it grows as an epiphyte on trees. It is often found in association with other lichens, such as Parmotrema, and bryophytes, such as Frullania. A main characteristic that distinguishes it from other closely related species is its clearly defined internal layers, including its contrasting dense and a loose lower .
The lichen was formally described as a new species by lichenologists Robert Lücking and Einar Timdal in 2016. The type specimen was collected from a moist deciduous forest on Mount Kenya (Kirinyaga County, Central Province) at an elevation of . The species epithet honours Norwegian lichenologist Hildur Krog, "for her invaluable contributions to African lichenology". The type locality is quite rich in species, and Krog made nearly 200 collections there.
Dictyonema krogiae is a member of the Dictyonema sericeum species complex, a group of species sharing similar overall morphology, including shelf-like, filamentous lobes.
The thallus of the lichen is filamentous and forms semi-circular shapes that can range from adnate to projecting shelves up to across, with single lobes wide. The fibrils are densely arranged, horizontally radiating and parallel, and are a dark greenish-blue (aeruginous) color without or with indistinct spaces in between. The thallus has a thick, , irregularly interlaced medulla, known as a , which is visible as a narrow line along the margin and strongly contrasts with the aeruginous fibrils.
Viewed microscopically in cross-section, the thallus is 400âÂÂ500 üm thick and ecorticate, meaning that it lacks a distinct outer layer. The is fully exposed and well-defined, with a thickness of 100âÂÂ150 üm. The medulla, made up of very loosely woven hyphae, is 200âÂÂ300 üm thick, and there is a lower "cortex" composed of more densely woven hyphae that is about 50 üm thick. The photobiont layer consists of numerous, arranged, parallel fibrils formed by cyanobacterial filaments wrapped in a closed hyphal sheath of jigsaw-puzzle-shaped cells. The fibrils are 15âÂÂ20 üm wide, with a hyphal sheath that is 2âÂÂ3 üm thick. The cyanobacterial filaments are composed of 12âÂÂ15 üm wide and 5âÂÂ7 üm high, aeruginous green cells penetrated by tubular fungal hyphae. The , sparse in distribution and ranging from hyaline to yellowish, measure 11âÂÂ13 üm wide and 4âÂÂ6 üm high. Cells of the hyphal sheath, undulating in profile, have a diameter of 3âÂÂ5 üm. In surface fibrils and towards the thallus margin, they are often shallowly -. The hyphae of the medulla, lower "cortex" (hypothallus), and white bordering line (prothallus) are straight, much branched, and 4âÂÂ6 üm thick, lacking clamp connections.
In Dictyonema krogiae, the hymenophore, which is the spore-producing structure, is only modestly developed. It manifests as soft, irregular patches of effuse or flattened growth on the thallus underside, bearing resupinate characteristics. These patches have a diameter of 0.5âÂÂ1 mm, are slightly convex, and have a whitish, smooth surface with indistinct margins. Viewed in microscopic cross-section, the hymenophore is 70âÂÂ150 üm thick and is composed of a tissue layer resting on strongly agglutinated, 4âÂÂ6 üm thick, generative hyphae that emerge from the supporting thallus. The hymenium is composed of numerous, palisade-like basidioles and scattered basidia. The basidioles are 20âÂÂ30 by 5âÂÂ6 üm, and the basidia are 30âÂÂ40 by 5âÂÂ7 üm and have 4 sterigmata. Only a few basidiospores have been documented; they are ellipsoid, hyaline, lack any septa, and measure 7âÂÂ10 by 3âÂÂ4 üm.