TUBER GENNADII (Chatin) Patouillard
Bull. Soc. Mycol. Fr. 19: 255 (1903)
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Synonyms:
Terfezia gennadii Chatin, Bull. Soc. bot. Fr. 43: 613, fig. p. 616 (1896)
Tuber lacunosum Mattirolo, Malpighia 14: 46, tab. I fig. 23–27 (1900)
Loculotuber gennadii (Chatin) Trappe, Parladé & I.F. Alvarez, Mycologia 84(6): 927 (1992)
Macroscopic characters:
Ascomata: hypogeous, subglobose or irregular in form, lobed, deeply sulcate, 1-5 cm in size, dirty white at first, then light brown, smooth.
Gleba: friable, solid, whitish at first, becoming light grey, light brown at maturity, marbled with numerous, thin, white, meandering veins. Characteristically loculate, sometimes showing a spongy appearance, more evident in exsiccata.
Odour: distinctive, faint when harvesting.
Taste: pleasant, not very persistent.
Habitat
Sandy soils with a Mediterranean climate, sharing habitat with Terfezia spp. They ripen in spring. Tuber gennadii is found associated with Tuberaria guttata and Helianthemum spp. in open pastures without trees.
Notes:
Tuber gennadii is a little-known truffle, often confused with Tuber asa Tulasne & C. Tulasne (1851). In the original description of Tuber asa, spores are globose and there is no mention of citriform or eye-shaped spores. According to Alvarez et al., who examined the holotype of Tuber asa, they found no eye-shaped spores or glebal chambers, but globose spores with a reticulum 2.5–4 µm high. Most determinations of Tuber asa in Spain describe the presence of eye-shaped spores. If the above considerations are taken into account, such specimens should be referred to as Tuber gennadii.
Tuber asa Tul. & C. Tul. appears to be a rare species, with very few collections and widely misunderstood. A specimen of Tuber asa preserved in Mattirolo's herbarium, sent by Ferry de la Bellone, was reviewed by Trappe in 1968 and determined as Delastreopsis oligosperma (= Tuber oligospermum).
Tuber gennadii is edible but of little gastronomic value.
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Microscopic characters:
Asci: ellipsoid to clavate or pyriform, thick-walled (1-3 µm thick), long stalked (up to 100 µm), more or less arranged among paraphyses in a hymenium, 90-150 x 50-70 µm excluding stalk, 1-3 (-4)-spored (usually 2-3-spored).
Ascospores: 28-43 x 27-40 µm excluding ornament, size variable depending on number of spores in the ascus, Q range = 1,00-1,37, globose to broadly ellipsoid or citriform, yellow, yellow brown at maturity, translucent, ornamented with a regular reticulum with polygonal meshes 4-5 (-7) µm high, 7-10 µm long, 4-6 across width of spore.
Peridium: 200–500 µm thick, composed of agglutinated, interwoven, hyaline hyphae mixed with subglobose cells in the innermost layer. The outermost layer may be entirely composed of hyphae, with emanating hyphae sometimes visible.
Glebal tissue composed of interwoven, hyaline hyphae.
Notes: Considerable variation in spore shape was observed across the various collections, some with very few eye-shaped spores and many globose spores (Q = 1.00–1.06).
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