Fossil evidence for Paleocene diversification of Araceae: Bognerospadix gen. nov. and Orontiophyllum grandifolium comb. nov.

Abstract

Premise: Nearly 200 araceous leaves and two spadices have been identified among Paleocene fossils from the Blindman River locality near Blackfalds, Alberta, Canada. Although not found in attachment, these probably represent parts of the same extinct plant species. Methods: Specimens were studied using light microscopy. Phylogenetic analyses using a morphological matrix of living and fossil Araceae were performed using TNT version 1.5 to help establish relationships of the fossil leaves and spadices within Araceae and to each other. Results: Leaves are simple with a broad petiole, entire margin, and elliptic to ovate or oblong blade with an acute to slightly rounded apex. A multi-veined midrib extends into the basal region of the blade. Parallelodromous primary veins of two orders diverge at acute angles, converging with a submarginal vein or at the apex. Transverse veins are opposite percurrent, producing rectangular to polygonal areoles. Higherorder veins are mixed opposite/alternate. Spadices are cylindrical, with helically arranged, bisexual, perigoniate flowers, each with six free tepals and a protruding style. Fruits are trilocular, with axile placentation and one seed per locule. Conclusions: Leaves are assignable to the fossil genus Orontiophyllum J. Kvaček & S.Y. Sm. as O. grandifolium comb. nov. Spadices are described as Bognerospadix speirsiae gen. et sp. nov. Leaves and spadices each conform to an early-diverging lineage of Araceae, increasing the known diversity of Proto-Araceae (viz., subfamilies Gymnostachydoideae and Orontioideae). Together, they provide strong evidence for extinct Proto-Araceae with novel combinations of characters shortly after the Cretaceous-Paleogene floral transition.

Lemnaceae and Orontiaceae Are Phylogenetically and Morphologically Distinct from Araceae

“…A morphological phylogenetic analysis of extant Arales [5] identified several features that are diagnostic or nearly so for Orontiaceae, including a collenchyma type [112] that is found only in Lysichiton and Symplocarpus, coincidentally the same two Orontiaceae genera whose inflorescence spathes otherwise make them appear superficially more similar to Araceae s.s. (petiole collenchyma is absent in Gymnocarpus and Orontium). Perhaps most noteworthy, there are leaf shape and venation patterns that can enable confident identification of Orontiaceae species, even in fossil material [113,114]. Thus, under more careful examination, there are more than a few characters that contradict the apparent similarity between Araceae s.s. and Orontiaceae.…”

Target sequence data shed new light on the infrafamilial classification of Araceae

“…It also has a remarkable fossil history, including some of the earliest known records for monocots, stretching back to the early Cretaceous (Friis et al, 2004, 2010; Hesse and Zetter, 2007; Bogner, 2009; Mayo et al, 2013; Smith, 2013; Iles et al, 2015; Hoffman, 2021). A recent review found that the family was particularly diverse during the late Cretaceous and early Paleocene (Stockey et al, 2021). Nauheimer et al (2012), using a molecular analysis combined with fossil data and computational modeling, concluded that the early evolution of the family was linked to aquatic or subaquatic environments and that early diversification within the family, which led to the evolution of subfamilial lineages, took place during the Cretaceous and was associated with the fragmentation of the supercontinent Pangaea.…”

“…. A recent review found that the family was particularly diverse during the late Cretaceous and early Paleocene (Stockey et al, 2021). Nauheimer et al (2012), using a molecular analysis combined with fossil data and computational modeling, concluded that the early evolution of the family was linked to aquatic or subaquatic environments and that early diversification within the family, which led to the evolution of subfamilial lineages, took place during the Cretaceous and was associated with the fragmentation of the supercontinent Pangaea.…”