Closed pileus up to 10 x 7 mm, ochre-coloured at centre, paler towards margin, up to c. 18 mm in diam. when expanded. Lamellae free, narrowly, white to blackish; L = c. 12-20, l = 0-1 (-3). Stipe 30-70 x 0.5-2 mm, whitish, pubescent.
Spores [40,2,2] 7.9-11.4 x 5.2-6.7 µm, av. L= 8.7-9.2, av. B= 5.3-5.4 µm, Q= 1.50-1.90, av. Q= 1.65-1.70, ovoid, somewhat truncate; germ pore central, c. 1.4 µm wide. Basidia 16-30 x 8-11 µm, 4-spored. Pseudoparaphyses (3-)4-5(-6) per basidium. Cheilocystidia 40-60 x 20-30 µm, globose to ellipsoid, ovoid or oblong. Pleurocystidia 60-120 x 15-35 µm, ellipsoid, ovoid, obovoid, oblong, (sub)cylindrical or slightly utriform. Pileocystidia 20-65 x 7-14 µm, lageniform with tapering neck, 2.5-5 µm wide at apex. Sclerocystidia absent. Clamp-connections absent.
The main characters, separating this species from others in the 'Setulosi', are the roundish apex of the spores and the central germ pore. The other species with this characters is C. pellucidus, but that has no pleurocystidia and its cheilocystidia are more globose and smaller. Moreover, C. pellucidus has very small fruit-bodies.
M. Lange (1952: 115) described C. stellatus with spores measuring 8.8-12.1 x 4.9-5.9 µm (averages per sample), Buller (original description) found them to measure 8-10 x 4-5 µm. In view of the narrow species concept in the Setulosi Arnolds preferred to describe C. stellatus sensu M. Lange as a new species on account of the different spore sizes and the somewhat deviating colour of the pileus (slightly more reddish) with the name C. brevisetulosus.
The first author (Uljé) studied the type of C. brevisetulosus and found the difference in size of the spores in comparison to those of C. stellatus sensu Buller somewhat smaller. Two times a sample of 20 spores was measured and the sizes found are: 7.9-9.9 x 4.9-5.8 µm and 8.0-10.2 x 5.0-6.0 µm. Arnolds found them to be 9.0-10.6 x 5.2-5.6 µm.
The diagnosis of C. brevisetulosis Arnolds gave the following spore sizes: (7.7-) 8.9-11.4 (-12.0) x 4.6-6.7 (-7.0) µm, probably compiled from those of the type and the four paratypes (Arnolds 3381, 3437, 3440 en 3579). In Arnold's notes with these collections the measurements are: (3381) 8.6-10.8 x 4.8-5.7 µm (3440) 9.5-11.4 x 6.0-6.7 µm (3437) 8.7-9.8 x 5.2-6.0 µm (3579) 8.6-10.2 x 4.6-5.4 µm
From these data it appears that the length of the spores of the type of C. brevisetulosus and the collections Arnolds 3437, 3579, and to a lesser degree also of 3381 agrees fairly well with the length of the spores of C. stellatus given by Buller. The breadth of the spores of these collections, however, agrees better with that given by M. Lange; the same applies to the length of the spores of Arnolds 3440.
The differences in spore size between C. stellatus and C. brevisetulosus is then mainly restricted to the breadth of the spores: values of about 0.5-1 µm.
We think that these differences are too insignificant to justify the maintenance of C. brevisetulosus as a separate species. Moreover, it is possible that Buller measured the spores in side view, whereas we and perhaps also other authors did that in front view. Because of the great variation in the colours of the pileus in subsection Setulosi the possible slight difference in pileus colour mentioned by Arnolds is even less convincing.