Original paper

Inflorescence and floral morphology in Tofieldia (Tofieldiaceae) compared with Araceae, Acoraceae and Alismatales s.str.

Remizova, Margarita; Sokoloff, Dmitry

Abstract

In recent time the taxonomic relationship of Tofieldiaceae was revised due to molecular data. Together with Araceae s.str. Tofieldiaceae was included in Alismatales. In order to establish whether morphological data agree with molecular ones, inflorescence and flower structure of Tofieldia were studied. Alismatales s.str. and Tofieldiaceae have similarities in gynoecium and androecium structure, but these features are insufficient to confirm the placement of Tofieldiaceae into Alismatales s.l. We found additional features shared by Tofieldia and some of Alismatales s.str., Araceae and Acoraceae. In Tofieldia, as well as in species of Araceae with trimerous flowers, the outer median tepal occupies adaxial position (in the majority of monocots its position is abaxial). Tofieldiaceae is characterised by presence of the structure, usually described as calyculus, at the pedicel. The calyculus typically consists of three free or connate scales. Calyculus of Tofieldiaceae resembles the "spathe" of Hydrocharitaceae and (pseudo)whorls of bracts in Alismataceae. However, the calyculus exhibits also important features of perianth whorl. The situation may be compared to some Alismatales where an exact "boundary" between structures of "flower" and "inflorescence" is often scarcely recognisable. A tendency to produce organs combining features of subtending bract and the first median abaxial phyllome on the pedicel is shared by Tofieldia pusilla, Acorus, Juncaginaceae, and some Potamogetonaceae. Our data support inclusion of Tofieldiaceae into the expanded order Alismatales.