The North American Slime-Moulds / A Descriptive List of All Species of Myxomycetes Hitherto Reported from the Continent of North America, with Notes on Some Extra-Limital Species

by Thomas H. Macbride

The distinction between the two genera is almost an artificial one, and species are sometimes arbitrarily assigned to one genus or the other. The diagnosis in any case turns upon the presence or absence of a surface net, formed, in Stemonitis, by the anastomosing of the ultimate divisions of the capillitial branches. In Comatricha the anastomosing is general, from the columella out, and is not specialized at the surface.

Recent attempts to reunite the genera here compared seem to result in no apparent advantage. The genera come very near together, but their separation along the line suggested by Rostafinski remains convenient.

Key to the Species of Comatricha

A. Sporangia closely clustered.
	a. Obovate or short cylindric.
		1. Spores verruculose			1. C. caespitosa
		2. Spores reticulate			2. C. cylindrica
	b. Elongate, reddish-brown, tufts extended				3. C. flaccida
B. Sporangia scattered more or less widely.
	a. Capillitium lax, open.
		i. Sporangia long, 10–12 mm.			4. C. longa
		ii. Sporangia shorter, capillitium irregular			5. C. irregularis
	b. Capillitium dense.
		i. Sporangia large, to 10 mm., spore-mass black			7. C. suksdorfii
		ii. Sporangia smaller—6 mm.
			O Spore-mass brown, spherical, conoidal, etc., generally with more or less lengthened stipe		8. C. nigra
			OO Spore-mass violaceous or purplish		9. C. aequalis
		iii. Sporangia ovate or cylindric, minute, to 3.5 mm.
			O Cylindric, spore with few, scattered warts		10. C. typhoides
			OO Smaller, capillitium irregular, loose		6. C. laxa
			OOO Total height to 2 mm. or much less.
				+ Columella digitately divided	11. C. elegans
				++ Columella lamprodermoid, and on leaves	12. C. rubens
				+++ Columella stemonitoid	13. C. pulchella
				++++ Columella furcate at tip	14. C. ellisii
				+++++ Columella almost percurrent.	15. C. subcaespitosa

1. Comatricha cæspitosa Sturgis.

[Plate XI.], Figs. 12, 13, 14.

• 1893. Comatricha caespitosa Sturg., Bot. Gaz., XVIII., p. 186.
• 1894. Diachaea thomasii Rex, var., List., Mycetozoa, p. 92.
• 1899. Comatricha caespitosa Sturg., Macbr., N. A. S., p. 124.
• 1911. Diachaea caespitosa Lister, Mycetozoa, 2nd ed., p. 121.

Sporangia densely crowded or cespitose, sub-sessile or short stipitate, clavate, 1–1.5 mm. high, the peridium gray, iridescent with blue tints, comparatively permanent but finally disappearing; columella attaining two-thirds to three-fourths the height of the sporangium, giving rise throughout its length to the dense blackish capillitium; hypothallus delicate, inconspicuous; capillitium, the main branches thick at the point of origin, frequently anastomosing, and becoming gradually thinner toward the surface of the sporangium, the tips pointed, free, forming the network; spores blackish-violet in mass, by transmitted light pale brownish-violet, rough, 9.5–13 µ.

A very distinct and curious species. The sporangia are densely crowded, though by the nature of habitat somewhat tufted. The shape of the individual sporangium is quite uniformly clavate or obovate, decidedly truncate above. The spores are uniformly verruculose and plainly unequal.

This species, as indicated, was by its author described as a comatricha. To transfer it to another genus seems idle, especially when long established generic boundaries must be seriously disturbed expressly to admit the new arrival.