Soleredera rhizomorpha gen. et sp. nov., a Permineralized Monocotyledon from the Middle Eocene Princeton Chert of British Columbia, Canada

Small permineralized monocotyledonous rhizomes and aerial stems from the Middle Eocene Princeton chert in British Columbia are described and named Soleredera rhizomorpha gen. et sp. nov. Rhizomes are up to 1.3 cm wide, have a narrow cortex without vascular bundles, and show a central cylinder composed of three or more irregular cycles of primary vascular bundles embedded in compact thick-walled ground tissue. The central cylinder surrounds a hollow or sometimes solid pith and is separated from the cortex by an endodermoid layer. Rhizome vascular bundles are collateral or amphivasal and lack a fibrous bundle sheath. Metaxylem consists of angular tracheids 9-42 μm wide with scalariform, transitional, opposite, or mostly alternate intervascular pitting. Pit apertures are lined with vesture-like projections. Attached to the rhizomes are lateral branches 2-3 mm wide and roots 0.5-1.5 mm wide. Aerial stems differ from the rhizomes in having two to three cycles of collateral bundles, tracheids with mostly scalariform lateral wall pitting, and ground tissue with relatively large intercellular spaces. Also, the aerial stems lack an endodermoid layer, cortex, and roots. Anatomical comparisons to extant monocotyledons show that the stems closely resemble several lilialean families (Liliaceae, Iridaceae), but lack of leaves and floral parts of Soleredera precludes its assignment to a family. Nevertheless, these vegetative remains are the first anatomically preserved lilialean megafossils from Middle Eocene deposits in North America to be described. Discovery of Soleredera adds to our knowledge of vegetative anatomy, morphology, and diversity of monocotyledons in the early Tertiary of western North America.