This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
In the genus Paxillus the gills are usually easily separated from the pileus, though there are some species accredited to the genus that do not seem to possess this character in a marked degree. The spores are ochre or ochre brown. Often the gills are forked near the stem or anastomose, or they are connected by veins which themselves anastomose in a reticulate fashion so that the meshes resemble the pores of certain species of the family Polyporaceae. The pileus may be viscid or dry in certain species, but the plant lacks a viscid universal veil. The genus is closely related to Gomphidius, where the gills are often forked and easily separate from the pileus, but Gomphidius possesses a viscid or glutinous universal veil. Peck in the Bull. N. Y. State Mus. Nat. Hist. 2: 29-33, describes five species.
Paxillus involutus (Batsch.) Fr. Edible. - This plant is quite common in some places and is widely distributed. It occurs on the ground in grassy places, in the open, or in woods, and on decaying logs or stumps. The stem is central, or nearly so, when growing on the ground, or eccentric when growing on wood, especially if growing from the side of a log or stump. The plants are 5-7 cm. high, the cap 3-7 cm. broad, and the stem 1-2 cm. in thickness. The plant occurs from August to October.
The pileus is convex to expanded, and depressed in the center. In the young plant the margin is strongly inrolled, and as the pileus expands it unrolls in a very pretty manner. The young plant is covered with a grayish, downy substance, and when the inrolled margin of the cap comes in contact with the gills, as it does, it presses the gills against this down, and the unrolling margin is thus marked quite prominently, sometimes with furrows where the pressure of the gills was applied. The color of the pileus varies greatly. In the case of plants collected at Ithaca and in North Carolina mountains the young plant when fresh is often olive umber, becoming reddish or tawny when older, the margin with a lighter shade. As Dr. Peck states, "it often presents a strange admixture of gray, ochraceous, ferruginous, and brown hues." The flesh is yellowish and changes to reddish or brownish where bruised. The gills are decurrent, when young arcuate, then ascending, and are more or less reticulated on the stem. They are grayish, then greenish yellow changing to brown where bruised. The spores are oval, 7-9 x 4-5 µ. The stem is short, even, and of the same color as the cap.
Paxillus involutus. Cap and stem gray, olive-brown, reddish brown or tawny (natural size). Copyright.
Plate 52, Figure 160
Paxillus rhodoxanthus. Cap reddish brown, stem paler, gills yellow (natural size). Copyright.
At Ithaca, N. Y., the plant is sometimes abundant in late autumn in grassy places near or in groves. The Figure 159 is from plants (No. 2508 C. U. herbarium) growing in such a place in the suburbs of Ithaca. At Blowing Rock, N. C, the plant is often very abundant along the roadsides on the ground during August and September.
Paxillus rhodoxanthus (Schw.) - This species was first described by de Schweinitz as Agaricus rhodoxanthus, p. 83 No. 640, Synopsis fun-gorum Carolina superioris, in Schriften der Naturforschenden Gesell-schaft 1 : 19-131, 1822. It was described under his third section of Agaricus under the sub-genus Gymnopus, in which are mainly species now distributed in Clitocybe and Hygrophorus. He remarks on the elegant appearance of the plant and the fact that it so nearly resembles Boletus subtomcntosus as to deceive one. The resemblance to Boletus subtomcntosus as one looks upon the pileus when the plant is growing on the ground is certainly striking, because of the reddish yellow, ochraceous rufus or chestnut brown color of the cap together with the minute tomentum covering the surface. The suggestion is aided also by the color of the gills, which one is apt to get a glimpse of from above without being aware that the fruiting surface has gills instead of tubes. But as soon as the plant is picked and we look at the under surface, all suggestion of a Boletus vanishes, unless one looks carefully at the venation of the surface of the gills and the spaces between them. The plant grows on the ground in woods. At Blowing Rock, N. C, where it is not uncommon, I have always found it along the mountain roads on the banks. It is 5-10 cm. high, the cap from 3-8 cm. broad, and the stem 6-10 mm. in thickness.
The pileus is convex, then expanded, plane or convex, and when mature more or less top-shaped because it is so thick at the middle. In age the surface of the cap often becomes cracked into small areas, showing the yellow flesh in the cracks. The flesh is yellowish and the surface is dry. The gills are not very distant, they are stout, chrome yellow to lemon yellow, and strongly decurrent. A few of them are forked toward the base, and the surface and the space between them are marked by anastomosing veins forming a reticulum suggestive of the hymenium of the Polyporaceae. This character is not evident without the use of a hand lens. The surface of the gills as well as the edges is provided with clavate cystidia which are filled with a yellow pigment, giving to the gills the bright yellow color so characteristic. These cystidia extend above the basidia, and the ends are rounded so that sometimes they appear capitate. The yellow color is not confined to the cystidia, for the sub-hymenium is also colored in a similar way. The spores are yellowish, oblong to elliptical or spindle-shaped, and measure 8-12 x 3-5 µ . The stem is the same color as the pileus, but paler, and more yellow at the base. It is marked with numerous minute dots of a darker color than the ground color, formed of numerous small erect tufts of mycelium.
Figure 160 is from plants (No. 3977 C. U. herbarium) collected at Blowing Rock, N. C, during September, 1899. As stated above, the plant was first described by de Schweinitz as Agaricus rhodoxanthus in 1822. In 1834 (Synop. fung. Am. Bor. p. 151, 1834) he listed it under the genus Gomphus Fries (Syst. Mycolog. 319, 1821). Since Fries changed Gomphus to Gomphidius (Epicrisis, 319, 1836-1838) the species has usually been written Gomphidius rhodoxanthus Schweinitz. The species lacks one very important characteristic of the genus Gomphidius, namely, the slimy veil which envelops the entire plant. Its relationship seems rather to be with the genus Paxillus, though the gills do not readily separate from the pileus, one of the characters ascribed to this genus, and possessed by certain species of Gomphidius in even a better degree. (In Paxillus involu-tus the gills do not separate so readily as they do in certain species of Gomphidius.) Berkeley (Decades N. A. Fungi, 116) has described a plant from Ohio under the name Paxillus flavidus. It has been suggested by some (see Peck, 29th Report, p. 36; Lloyd, Mycolog. Notes, where he writes it as Flammula rhodoxanthus!) that Paxillus flavidus Berk., is identical with Agaricus rhodoxanthus Schw.
Paxillus rhodoxanthus seems also to be very near if not identical with Clitocybe pelletieri Lev. (Gillet, Hymenomycetes 1: 170), and Schroeter (Cohn's Krypt, Flora Schlesien, 3, 1 : 516, 1889) transfers this species to Paxillus as Paxillus pelletieri. He is followed by Hennings, who under the same section of the genus, lists P. flavidus Berk., from N. A. The figure of Clitocybe pelletieri in Gillet Hymenomycetes, etc., resembles our plant very closely, and Saccardo (Syll. Fung. 5: 192) says that it has the aspect of Boletus subtomento-sus, a remark similar to the one made by de Schweinitz in the original description of Agaricus rhodoxanthus. Flammula paradoxa Kalch. (Fung. Hung. Tab. XVII, Fig. 1) seems to be the same plant, as well as F. tammii Fr., with which Patouillard (Tab. Anal. N. 354) places F. paradoxa and Clitocybe pelletieri.