Liriodendron (Magnoliaceae) from the Miocene Clarkia Flora of Idaho

Abstract

Miocene Liriodendron carpels, whole fruiting structures and leaves from Clarkia and Oviatt Creek sites in northern Idaho are preserved as imprints and compressed fossils in soft lacustrine clays. The isolated carpels are indistinguishable from those described as L. hesperia Berry from the Spokane Latah flora. Fruit aggregates from the type Clarkia and Oviatt Creek localities and leaves from three Clarkia sites are considered to be within the range of variation of the single species L. hesperia. Comparisons were made regarding leaf architecture, lower leaf epidermal structures, leaf flavonoid and steroid analysis, morphological features of receptacles and carpels, and the venation pattern of carpels of the fossil material to the two extant species, L. tulipifera L. (native to southeastern United States) and L. chinense Sarg. (native to southeastern Asia). Leaf architecture features analyzed by standard statistical and canonical tests and marginal venation patterns near the base of leaves suggest that L. hesperia is more similar to L. tulipifera, whereas the size dimensions of lower epidermal cells and the common presence of two sterane compounds imply that L. hesperia is more similar to L. chinense. The fossil species, however, is a distinct taxon indicated by statistical discriminant and canonical tests, leaf base shape, often smaller epidermal cell dimensions, and the shape of round receptacle carpel scars. Both the fossil and the two living Liriodendron species are associated with comparable mixed mesophytic floras.