When published, the fossil-genus included in synonymy several validly published fossil-generic names, viz. Thujoxylon Unger (Chlor. Protogaea ed. 1842, (2-3): 31. 16 Apr 1843 [all fossil-species from protologue]), Calloxylon Andrae (in Bot. Zeitung (Berlin) 6(36): 633. 8 Sep 1848) and Physematopitys Goepp. (in Natuurk. Verh. Holl. Maatsch. Wetensch. Haarlem, Ser. 2, 6: 242. 10 May 1850).