Fig. 2

Morphological and structural observations of floral organs. a Fertile (VMF) and sterile (VMS) flowers of V. macrocephalum f. keteleeri observed by digital camera from early to late April. Scale bar: 1 cm. b Cellular morphology of VMF (d–e) and VMS (a–c) at three different developmental stages. Scale bars: 50 μm. c Anatomical features of VMF (d–e) and VMS (a–c). Red arrows indicate the short stamens (a), abnormal stamens (b), and the abnormal embryo sac with cavity in the ovary (c) of VMS. Black arrows indicate the normal stamens (d), stamens with anthers (e), and normal embryo sacs (f) of VMF. S: stamen, E: embryo sac, P: pistil, PG: pollen grain, AS: anther septa. Scale bars in a, b, d, and e: 0.5 mm; scale bars in c and f: 0.2 mm. d Petal areas of VMF and VMS. e Cell counts of VMF and VMS. f Cell areas of VMF and VMS