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Ascomycetes on bryophytes: systematics and biology

Hyphal and ascospore features

Apart from ascoma and ascus types hyphal and ascospore features are also beneficial in recognizing biological or systematic affinities. They demonstrate the enormous heterogeneity of bryophilous species related to many non-bryophilous ascomycetes. Hyphae of biotrophic parasites can grow over the host cell walls or within them or between them. In some cases, as in Bryochiton perpusillus on Polytrichaceae, the hyphae are covered by the cuticle. Superficial hyphae often follow the path of the anticlinal host cell walls resulting in a hyphal net that corresponds to the host’s cell wall arrangement. Intercellular hyphae may be restricted to the anticlinal walls and the cell corners or grow irregularly within the cell walls. In contrast, all analysed necrotrophic parasites have an intracellular mycelium that grows from cell to cell perforating the periclinal walls in leaves using delicate perforation hyphae.

Several types of appendages can be found on the hyphae, such as appressoria, haustoria or a combination of both, and conidiogeneous cells. Lateral sessile appressoria are a generic character of Bryonectria. Dawsomyces has one-celled appressoria with delicate radial structures similar to those of Discinella schimperi on Sphagnum squarrosum. Its appressoria closely adhere to the internal wall of the mucilaginous cells in the shoot apex.

The superficial hyphae of Bryothele mira and Gloeopeziza cuneiformis form intracellular haustoria without appressoria. Complex infection structures with appressoria and haustoria occur in species of Hypobryon, Leptomeliola, and in Octospora and related genera. Conidiogeneous cells at the hyphae have been seen sporadically in species of Bryonectria and Hypobryon and in Epibryon filiforme and E. hepaticola.

The ascospores exhibit an astonishing diversity. Many spore types are assembled here that occur in non-bryophilous species of quite different systematic position and ecology. They vary in shape (globose to filiform), size (4 to 50 µm in diameter – in ellipsoid spores), septation (one-celled or with many transverse septa or muriform types), colour (colourless to light or dark brown) and other features like presence of oil bodies, appendages, cyanophilic reactions, and formation of partial spores. Acrospermum adeanum has filiform septate spores up to 350 µm long. Circular germ slits at both ends of the dark brown, thick-walled spores occur in Bryothele mira. The very small fertile spore of Anthonectria mammispora is situated at the top of an umbrella-like appendage without any plasmatic content. Gynonectria intraspora is remarkable for its intraspores that are formed within the mother spores retaining residual primary spore plasma around them. Bryocentria merospora has disarticulating spores that behave in a curious manner. The dimorphic partial spores begin to segregate within the ascus resulting in a concentration of the smaller globose spores in the ascus apex while the larger pin-shaped spores remain in the middle and lower part of the ascus. The latter four species are parasitic on tropical epiphyllous hepatics. They appear to be undergoing an active evolutionary diversification, as are their mostly lejeuneaceous hosts.

Ascospores of all known ten species of ascomycetes on Frullania dilatata from Tuscany. Mycol. Progess 5: 33 (2006).

  1. Broycentria brongniartii
  2. Bryonectria callicarpa
  3. Calonectria frullaniae
  4. Epibryon perrumpens
  5. Hypobryon florentinum
  6. Muellerella frullaniae
  7. Muellerella rubescens
  8. Nectria lagodes
  9. Octosporella erythrostigma
  10. Pithyella frullaniae

Ascospore types of hyperepiphyllous ascomycetes (35 species known, several not yet formally described).

  1. Octosporella radulae
  2. Octosporella epiphylla
  3. Nectria gynophila
  4. Nectria contraria
  5. Bryorella "acicularis"
  6. Nectria lankesteri
  7. Nectria "mons-viridis"
  8. Bryocentria aequinoctialis
  9. Nectria hyperepiphylla
  10. Bryocentria manubriata
  11. Bryonectria protonematis
  12. Ticonectria perianthii
  13. Gynonectria intraspora
  14. Nectria brenesii
  15. Ticonectria testudinea
  16. Anthonectria mammispora
  17. Bryothele mira
  18. Bryonectria clandestina
  19. Bryocentria merospora
  20. Epibryon hypophyllum
  21. Hypobryon insigne
  22. Epibryon deceptor
  23. Epibryon filiforme