Camarophyllopsis hymenocephala (A. H. Sm. & Hesler) Arnolds, Mycotaxon 25: 643. 1986.
= Hygrophorus hymenocephalus A. H. Sm. & Hesler, J. Elisha Mitchell Sci. Soc. 56:31. 1940.
= Camarophyllus hymenocephalus (A. H. Sm. & Hesler) M. Lange, Friesia 4: 1. 1950.
= Armillariella hymenocephala (A. H. Sm. & Hesler) Singer, Lilloa 22: 217. 1951.
= Hygrotrama hymenocephala (A. H. Sm. & Hesler) Singer, Sydowia 12: 222. 1959.
Selected Descriptions. Smith and Hesler (1940: 311); Hesler and Smith (1963: 103-105).
Pileus (Fig. 1) 8-17 mm diam, convex or obtusely and broadly conic when young, expanding with maturity to broadly convex, sometimes with a slight central depression, disc rugulose, margin pellucid-striatulate becoming crenulate in age; surface glabrous, moist to dry, dull, hygrophanous; when young brownish orange (5C4-5) or greyish orange (5B4-5) overall, fading in age and with moisture loss to pale greyish orange (5B3), orange white (5A2-3) or cream (4A3). Context relatively thick (-2 mm), buff. Lamellae adnate with a short decurrent tooth or subarcuate, subdistant to distant (16-18 per hymenophore) with 1-2 series of lamellulae, concave, broad (3-5 mm); when young ranging from light orange (5A4) or orange white (5A2-3) to buff with paler edges, becoming greyish orange (5B4), brownish orange (5C4), pale brownish grey (6C3) or light brown (6D4) in age, often with paler edges. Stipe 25-40 X 2-4 mm, central, round or compressed in cross-section, ± equal or with a slightly flared apex and subbulbous base; apex pruinose to furfuraceous, silky or glabrous centrally, base pubescent, dry, tough, hollow; white, buff or pale yellowish white overall when young, remaining so in age (not darkening), drying dark brown. Odor and taste not distinctive.
Basidiospores (Fig. 2) (4.8-)5.0-6.0(-6.4) X 4.5-5.5 µm [range of means = 5.4-5.7 X 4.9-5.2 µm, mean of means = 5.6 ± 0.2 X 5.1 ± 0.1 µm, Q = 1.0-1.3, mean Q = 1.10-1.13, mean of Q means = 1.11 ± 0.02, n = 20 spores per 3 specimens], subglobose to globose, seldom broadly ovoid, with a prominent broad hilar appendix, smooth, hyaline, inamyloid, thin-walled. Basidia (Fig. 3) 40-62 X 6.5-9.5 µm, 4-spored, slenderly clavate, mostly hyaline, some with golden brown contents, unclamped. Hymenial cystidia absent. Pileipellis (Fig. 4) a continuous to interrupted hymeniform layer of broadly clavate to sphaeropedunculate cells 24-45 X 8-20(-32) µm, thin-walled, nongelatinous, walls hyaline to pale yellowish brown, some with yellowish brown contents. Pileus trama of radially arranged, moderately compact hyphae 3-10 µm diam, cylindrical, smooth, nongelatinous, thin-walled, hyaline. Hymenophoral trama subregular; hyphae 15-70 X 3-10 µm, cylindrical to inflated, hyaline. Stipe tissue monomitic; cortical and medullary hyphae undifferentiated, 3-8 µm diam, parallel, cylindrical, smooth, nongelatinous, hyaline, inamyloid. Caulocystidia (Fig. 5) common on stipe apex, as recurved terminal cells of stipe cortical hyphae, cylindrical or irregular in outline, broadly obtuse, 5.5-10 µm diam, hyaline, thin-walled. Clamp connections absent in all tissues.
Habit, habitat and distribution. Scattered, in small clusters or rarely subcespitose, in soil among various grasses (including bamboo) under mixed introduced hardwoods in Lowland Mesic Forest. January. Kaua`i, O`ahu.
Specimens Examined. U.S.A. HAWAII: Kaua`i, Na Pali Coast State Park, Kalalau Trail, 13 Jan. 1991, DED 5055. O`ahu, Honolulu, Manoa Valley, Manoa Valley Trail, 8 Jan. 1992, DED 5451. NORTH CAROLINA: Macon Co., Highlands, 21 Aug. 1938 (incorrectly cited as 14 Aug. 1938 in protologue), A. H. Smith 10383 (Holotype; MICH).
Commentary. Camarophyllopsis hymenocephala belongs in subgen. Hodophilus (R. Heim) Arnolds, sect. Hodophilus (R. Heim ex R. Heim) Arnolds (sensu Arnolds, 1986b). The Hawaiian specimens match the holotype specimen in most details, differing mainly in the stipe coloration. The stipes of the Hawaiian specimens do not darken in age when fresh as is typical for North American C. hymenocephala, but rather become dark brown only when dried. Basidiospores of the holotype specimen (MICH!) measured 5.3-6 X (4.8-)5-5.7 µm (mean = 5.7 X 5.1 µm), slightly broader than those reported by Smith and Hesler (4-5 µm diam; 1963).
This species was reported by Ueki (1973; unpublished undergraduate honors thesis, Univ. of Hawai`i at Manoa) as Hygrotrama schulzeri (Bres.) Singer. The latter species is not known from the Hawaiian Islands. It differs in forming a trichodermium type of pileipellis with much narrower terminal cells and smaller basidiospores measuring 3-4(-5) X 2.5-3.5(-4) µm (fide Arnolds, 1990).
Camarophyllopsis hymenocephala has been collected only twice in the Hawaiian Islands, and both populations are associated with Lowland Mesic Forests dominated by alien plants. These data suggest that the species was probably introduced recently to the archipelago.
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