C3 and C4 leaf anatomy types in Camphorosmeae (Camphorosmoideae, Chenopodiaceae)

Abstract

Complementary to our previous project on the molecular phylogeny of Camphorosmeae, the leaf anatomy of ca. 35 species including all non-Australian and selected Australian species was studied by use of light microscopy. Nine anatomical leaf types were described, compared to previous classifications, and discussed with regard to their putative evolution on the background of phylogenetic trees. Particular emphasis was given to the relationships between the C3 and C4 leaf types: Chenolea type (C3), Eokochia type (C3), Neokochia type (C3), Sedobassia type (C3/C4 intermediate), Bassia prostrata type (C4), B. muricata type (C4), B. eriantha type, B. lasiantha type (C4), Camphorosma type (C4). The main results and conclusions were: (1) Two unusual new C3 leaf types: Chenolea with microfenestrate chlorenchyma, Eokochia with unique complex vascular bundles; (2) Sedobassia interpreted as anatomically C3/C4 intermediate by kranz-like bundle sheath cells is the first C3/C4 intermediate in Camphorosmeae and found in a derived position; (3) Neokochia type detected as the likely starting point for all four C4 leaf types and for the C3/C4 intermediate; (4) hypodermis of C4 types originated from outermost chlorenchyma layer of C3 types and lost multiple times during further evolution; (5) atriplicoid Bassia. lasiantha type without water storage tissue evolved from kochioid B. muricata type; (6) two independent gains of C4 photosynthesis, one in Bassia and one in Camphorosma; (7) depending on the lineage, leaf architecture remains comparatively stable (Australian Camphorosmeae) or shows an unexpected plasticity (Bassia scoparia group).