Rhytisma americanum

Family: Rhytismataceae | Genus: Rhytisma
Detachable: integral
Color: yellow, black
Texture: hairless, wrinkly
Abundance: abundant
Shape:
Season: Fall
Related:
Alignment: integral
Walls:
Location: upper leaf, lower leaf, between leaf veins
Form: non-gall, leaf spot
Cells:
Possible Range:i
Common Name(s):
Synonymy:
Slide 1 of 3
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum
image of Rhytisma americanum

Rhytisma americanum sp.nov.: a previously undescribed species of Rhytisma on maples (Acer spp.)

Rhytisma americanum, sp. nov.

Hosts: Acer rubrum, saccharinum, saccharum [later work by Hsiang et al suggests the Rhytisma on Acer saccharum is more likely R acerinum]

[R americanum] matures as circular masses of stromatic tissue rarely more than 10 mm in diameter. First symptoms of impending disease are chlorotic [yellow] spots that appear on new foliage in central NY state from mid-June to the first week in July. In the case of [R americanum], a small (<0.5 mm diam) black mass of fungal tissue [pycnidia] appears near the center of each spot. Pycnidia are detectable for no more than 3 weeks; thereafter the spots rapidly grow to become typical thickened black stromata comprised of fertile white fungus tissue overlain with a black rind. By autumn, from 2 to 12 parallel sinuous channels of ascogenous tissue are discernible by the depressions they case in the rind of each stroma. In many cases stromata are surrounded by a bright yellow border of chlorotic host tissue.

Stromata: on abaxial surfaces only of host leaves, black, more or less cylindrical except where limited by major veins, diam variable but rarely less than 3 mm or more than 10 mm, up to 1.5 mm thick at center and tapered to leaf surface at perimeter, occasionally surrounded by a bright yellow halo of chlorotic host tissue. In surface view: ascomata develop as parallel sinuous channels, extending up to the entire length of the stroma.

Habitat: on leaves of Acer rubrum, A saccharinum, and rarely, Acer saccharum, Common in North American east of the Great Plains, uncommon elsewhere.

- GW Hudler, S Jensen-Tracy, MT Banik: (1998) Rhytisma americanum sp.nov.: a previously undescribed species of Rhytisma on maples (Acer spp.)©

Reference: http://www.cybertruffle.org.uk/cyberliber/59575/0068/0412.htm


Further Information:
Pending...

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