Floral anatomy of Magnolia decidua (Q.Y.Zheng) V.S.Kumar (Magnoliaceae): recognition of a partial pentamery

Floral anatomy of the endemic Chinese species Magnolia decidua (Q.Y.Zheng) V.S.Kumar was studied in order to clarify its disputed relations within the family Magnoliaceae. Its most striking feature is a change in floral merosity, clearly demonstrated by the vasculature, the three perianth whorls being often pentamerous, while only the gynoecium might be considered as trimerous. Interestingly the androecium exhibits an intermediate condition, as the stamens are supplied by 15 vascular trunks, a pattern reminiscent of that previously described in Meiocarpidium Engl. & Diels (Annonaceae), with two levels of 15 trunks each. Perianth pentamery, almost completely lacking sclerenchyma at anthesis, as well as a sharp separation in the vascular supply of the perianth and sexual parts, characterize unmistakably this species from all other known Magnoliaceae, even though its relationship with Magnolia sect. Manglietia is otherwise strengthened by stamen and carpel pattern. This very unexpected pentamery – somewhat comparable to that of the monocot genus Pentastemona Steen. – is briefly discussed. The value of vascular anatomy as an additional but essential source of data to complement the standard phyllotactic and ontogenetic approaches used for the flower, is emphasized again.