Chaenothecopsis dolichocephala (Tibell and Titov 1995), C. golubkovae (Titov and Tibell 1993) and C. hunanensis are very similar to C. proliferatus. C. dolichocephala often produces branched and proliferating fruiting bodies, has similar colorless crystals in the hymenium, and also shares a similar anatomy of the stipe and exciple. However, its ascomata are on average smaller, the stipe is shinier and the ascospores are ornamented. The blue IKI + reaction is very faint or non-existing and

the red IKI + reaction occurs only Target Selective Inhibitor Library chemical structure in the lower part of exciple and stipe, if at all. The spore size, epithecial structure and the IKI + color reactions of C. golubkovae are more or less identical to those of C. proliferatus. However, C. golubkovae is characterized by the highly branched and irregularly shaped hyphae (textura epidermoidea) formed from fused cell walls of the exciple and stipe. C. PLX4032 in vivo hunanensis has slightly smaller spores with thin septa and a different type of epithecium when compared with C. proliferatus. The distinction between C. proliferatus, C. dolichocephala, C. golubkovae and C. hunanensis requires study of anatomical details and chemical features that cannot

be observed from fossil specimens embedded in amber. Hence, despite their excellent preservation, we do not want to assign the new fossils to any extant species, and we also refrain from assigning them to the previously described Chaenothecopsis bitterfeldensis Rikkinen & Poinar. However, the four extant species and the three fossils are obviously closely related and most probably belong to the same lineage since C. bitterfeldensis resembles C. proliferatus and the two newly discovered fossils in ecology and spore type (Rikkinen and Poinar 2000). The morphological similarities between C. proliferatus and the proliferating Carnitine palmitoyltransferase II fossil from Bitterfeld amber are especially striking. The only obvious difference is in the size of the fruiting bodies, with the preserved

ascocarps of the fossil being distinctly smaller than typical ascocarps of C. proliferatus. Both fungi have relatively slender, commonly branched and proliferating fruiting bodies. The shape and general appearance of the capitula of young fruiting bodies are also identical. The stipes of both fungi are lined by a net of arching and horizontal hyphae (compare Figs. 2a, c and 7d, e), and these hyphae extend to the epithecium in a similar way. In both fungi, the one-septate and smooth (or minutely punctate) ascospores accumulate on top of the epithecium. All these morphological features together indicate that the fossil is closely related to C. proliferatus. The epithecium of Chaenothecopsis proliferatus is, in places, covered by a thin layer of small crystals. These blade-like structures are typically 1–3 μm long and sharply pointed at both ends (Fig. 4d). While some crystals seem to be partly embedded in the extracellular matrix of fungal hyphae, most appear external.