A review of the Hirmeriellaceae (Cheirolepidiaceae) wood

The Hirmeriellaceae are an extinct family of Mesozoic conifers. Their foliage has been described in the genera Brachyphyllum, Frenelopsis, Pseudofrenelopsis, etc., while their pollen corresponds to the genus Classopollis, the male cones to e.g. Classostrobus or Tomaxellia and the female scales were named Hirmeriella and Paraucaria, for example. Reproductive structures are necessary for a definite identification of the family. Such fossils are rarely found in connection with mature secondary xylem. As a result, very little is known about the wood anatomy of the Hirmeriellaceae. This work reviews available evidences, either from connections between wood and reproductive structures typical for the Hirmeriellaceae or from associations of such fossils within Mesozoic rocks. Connection cases are rare and are reported only for the Cretaceous and for genera Frenelopsis and Pseudofrenelopsis. Association cases are more numerous; however, they are also poorly distributed in time, being reported mostly from two intervals only, the latest Triassic–earliest Jurassic and the Early Cretaceous. Wood data are also poorly distributed taxonomically with most of them being from the frenelopsids. The fossil genera Agathoxylon, Brachyoxylon, Protocupressinoxylon and Protopodocarpoxylon were used for wood fossils which are more or less safely related to the Hirmeriellaceae. However, only the first two seem to have been rightly used, the first usually for juvenile or small diameter wood, the second for more mature wood. Even if there seems to be a privileged link between Brachyoxylon and the Hirmeriellaceae, it cannot be said to be exclusive.