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Kubilius, Rimas A.; Bölz, Adrian; Feldberg, Kathrin; Hedenzaes, Lars; Schzaefer-Verwimp, Alfons; Schmidt, Alexander R.; Heinrichs, Jochen (2017): The moss Helicophyllum torquatum (Bryopsida: Helicophyllaceae) has survived since at least the Miocene. In: Botanical Journal of the Linnean Society, Vol. 185, No. 1: pp. 56-64
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Abstract

Classification of incompletely preserved fossils is a challenging task. We describe a moss fossil preserved in a piece of Miocene Dominican amber and assign it to the monospecific extant genus Helicophyllum. According to the published divergence time estimates, Helicophyllum originated in the Late Cretaceous, but so far no Helicophyllum fossils have been found. The Helicophyllum fossil consists of several sterile gametophytes with dimorphic leaves in two lateral and one ventral series;the lateral leaves being lingulate and obtuse and the shorter ventral leaves ovate-lanceolate. All leaves have a percurrent single costa and hexagonal to subquadrate, papillose cells. The fossil differs from extant Helicophyllum torquatum only by its slightly narrower leaf costa. Based on the extensive morphological overlap of the fossil and extant Helicophyllum specimens in other gametophytic characters and considering the Mesozoic origin of the genus, we propose an assignment of the fossil to the extant species H. torquatum, thereby accepting a minimum age of the species of 15 My. We discuss the problems of assigning fossils to extant species and propose to take into account not only morphological evidence but also evidence from divergence time estimates.