Pileus annual, sessile, 4-5.5 X 3-5 X 3-4.5 cm., dimidiate, ungulate, triquetrous in section, often imbricate or laterally confluent; at first `Dresden Brown', [Colour terms in quotes are from Ridgway, Color Standards and Color Nomenclature, 1912] `Tawny', or ferruginous, glabrous, soon developing a hard crust, becoming rimose, and at times radiately rugose especially towards the margin. Margin acute or obtuse, entire, undulate. Context up to 3 cm. thick, though thinner towards the margin. Characterized by a large core, situated at the base of the pileus; this may occupy a considerable proportion of the total volume, is of a granular nature, permeated throughout by white or yellowish flecks, and contains numerous conducting organs with yellowish or brownish contents. The remainder of the context which radiates out from the core is concentrically zoned, fibrous in texture, though watery and spongy when fresh, but soft and brittle when dry, and with a silky sheen. Colour varies from 'Buckthorn Brown' to `Tawny', but `Ochraceous Buff' or paler towards the pileus surface. Pore surface convex, often becoming concave towards the margin, ferruginous to dark umbrinous, narrowly sterile at the margin, usually covered by a cream-coloured pruina formed of secondary hyphae. Pores medium to large, irregular, round or angular, often becoming torn, 2-4 per mm., 170-620 µ diam., even. Tubes non-stratified, distinct from the context, ferruginous, but internally grey, brittle when dry, 2-14 mm. long; dissepiments 25-75 µ thick. Spores, few seen, 7.5-10 x 5.5-7 (8.5 x 6) µ, broadly ellipsoic; sometimes unilaterally flattened, with a small, lateral apiculus, smooth with a distinctly thickened, colourless or faintly brownish wall, occasionalh some found embedded within the tube layer or adhering to the pileus surface making it appear fulvous. Basidia large, colourless, 12-15 x 7-8 µ with 4 sterigmata. Setae present, not abundant, but occasionally localized in small groups, very thick-walled, but always with a lumen, dark chestnut-brown, appearing black in 10 % potassium hydroxide solution, 23-35 x 7-10 (-16) µ, ventricose to subulate. Setal hyphae absent. Context hyphae not agglutinated, dark ferruginous, with a thickened wall but a wide lumen, septate, branched, 4-10.5 µ, mostly about 5.5 µ diam. Tramal hyphae, tightly interwoven, not agglutinated, fulvous to ferruginous, very thin-walled, septate, rarely branched, 1.5-5 µ diam.

Pileus sessilis, dimidiatus, ungulatus, 4-5.5 cm. longus, 3-5 cm. latus, 3-4.5 cm. crassus. Superficies superior crusta glabra, ferruginea demum atrobrunnea; margine decurvato, obtuso vel acuto. Contextus usque 3 cm. crassus, brunneus sed crusta versus pallidus, radialiter fibrillosus, nucleo arenoso-granuloso praeditus. Tubuli 2-14 mm. longi; pori rotundati vel angulati, 2-4 per mm. (170-620 µ diam.), atro brunnei, dentati. Sporae 7.5-10 x 5.5-7 (8.5 x 6) µ, rarae, hyalinae, laeves, late ellipsoideae, muris crassis. Setae rarae, 23-35 X 7-10(-16) µ, muris brunneis crassis, ventricosae vel subulatae. Hyphae setoideae absunt. Hyphae contextus 4-10.5 µ diam., ramosae, septatae, crassitunicatae. Hyphae dissepimenti 1.5-5 µ diam., tenuitunicatae. Hab. in Eucalypto obliqua, Mt Lofty, South Australia. Ex-herb. J. B. Cleland. (Typus.)

This Australian species has hitherto passed under the name Inonotus dryadeus (Pers. ex Fr.) Murr. [as Polyporus dryadeus]. Cleland (1935),. following the advice given by Lloyd, used this name, though at the same time he suggested that his material might possibly not be the same as the European fungus. When a careful comparison is made of the Australian and European forms it becomes clear that a number of fundamental differences do occur, and that two species are involved though they are enough alike for the confusion in the past to be understandable. Both have a well-developed crust; the spores are large and colourless or nearly so; both have thick-walled, dark-staining setae; and apparently both are prone to exude watery droplets from the pileus surface.
The sporophore of I. chondromyelus, though often imbricate or laterally confluent, consists essentially of a medium-sized, ungulate pileus, which fruits high up on the trunk of the host, and this contrasts sharply with the large, more applanate habit of L. dryadeus, which fruits at or just above ground level. The spores of the former species, though similar in having a thickened wall, are broadly ellipsoid (8.5 x 6 µ) with a lateral apiculus, whereas those of L. dryadeus are subglobose (7.5 x 6.8 µ). The setae, too, are quite different in form, being straight and not curved with a larg, bulbous base. It is in the context that the most obvious distinctions are to be found: L. chondromyelus possesses a granular core, found at the base of the pileus because this is the first-formed structure of the fructification, and even though it may not be well developed it is nevertheless a constant feature which determines the thickness of the sporophore. In the remainder of the context the hyphae have thickened walls and a correspondinly narrower lumen. L. dryadeus never develops a core and the context is composed of thin-walled hyphae with a wide lumen. Other differences may be noted in the pore size and in the nature of the margin.
This species is known only from Australia, where it appears to be not uncommon and is apparently restricted to trunks of Eucalyptus (Walters,1955).