Fungalpedia – Note 3006, Densorhytisma
Densorhytisma C.L. Hou, Q.T. Wang & P.F. Cannon.
Citation when using this data: Wang QT et al. 2023 – Fungalpedia.
Index Fungorum, Faceoffungi, MycoBank, GenBank, Fig 1, 2.
Classification: Rhytismataceae, Rhytismatales, Leotiomycetidae, Leotiomycetes, Pezizomycotina, Ascomycota, Fungi.
Etymology: The name refers to the stromata that are densely covering the host leaves.
Parasitic on semi-evergreen Rhododendron simsii. Stromata developing on living leaves, strongly raising above the surface of the substrate, spreading over almost the entire surface of the leaf, irregular in shape, 0.25–1.2 mm diam. Ascomata opening by a longitudinal split or irregular split. Lips absent. Paraphyses filiform, unbranched, curved at the apex. Ascospores narrowly clavate to filiform, often curved, without gelatinous sheaths.
Notes: The Rhododendron clade Ⅰ is sister and corresponds to an independent clade with high support values in the phylogenetic tree (Wang QT et al. 2023). The two species of this clade are both parasitic on semi-evergreen Rhododendron simsii (Rhododendron subgenus Tsutsusi; Yang et al. 2020), parent of the widely cultivated indoor azalea. They have small ascomata which can spread over the entire surface of the leaf. Ascospores of species in this genus have no gelatinous sheaths. This subclade is suggested to be treated as a separate genus. Rhytisma rhododendri Fr. was first reported on Rho. stenopetalum (R. Hogg) Mabb. (syn. Rho. macrosepalum Maxim.) in Japan (Fries 1823), and was also reported on Rho. simsii and Rhododendron spinuliferum Franch. from China (Dai 1979). As dimensions of asci and ascospores were not given, this species could not be compared with others on Rhododendron L., and its affinity needs to be clarified with examination of modern collections. Rh. rhododendri-oldhamii Sawada is invalidly published as it lacked a Latin diagnosis. However, the characteristics of this species appear very similar to those of Densorhytisma, with small ascomata which can spread over the entire surface of the leaf (Tai 1979). Based on host and stromata as well as characteristics of ascomata, it should probably be treated as a further species of Densorhytisma, but new specimens need to be collected to confirm its correct taxonomic status.
Type species: Densorhytisma huangshanense (C.L. Hou & M.M. Wang) C.L. Hou, Q.T. Wang & P.F. Cannon.
Other accepted species: Species Fungorum – search Densorhytisma.
Figure 1 – Densorhytisma huangshanense on Rhododendron simsii (HOU 564/AAUF, holotype). a Ascomata on the adaxial surface of a leaf. b Immature ascomata. c Mature ascomata. Scale bars a = 2 cm, b = 500 μm, c = 500 μm.
Figure 2 – Densorhytisma huangshanense (HOU 564/AAUF, holotype). a Detail of a mature ascoma in vertical section. b Paraphyses, mature asci with ascospores, and immature asci. c Liberated ascospores. Scale bars a = 50 μm, b = 20 μm, c = 20 μm.
References
Dai FL. 1979 – Sylloge Fungorum Sinicorum. Beijing: Science Press. pp1–1577.
Fries EM. 1823 – Systema Mycologicum. 1: 259–572.
Tai FL. 1979 – Sylloge Fungorum Sinicorum. Beijing: Science Press.
Entry by
Qiu-Tong Wang and Mei-Jun Guo, College of Life Science, Capital Normal University, Xisanhuanbeilu 105, Haidian, Beijing 100048, China.
Published online 27 August 2026