Fig. 6.

Pseudanthium formation in Dichostemma glaucescens (SEM). (a–f) Early stages. (a) Young pseudanthium subtended by bract and preceded by two bracteoles in the median plane. Arrowhead points to a pseudanthial primordium in the axil of the abaxial bracteole. Two male elements and their subtending bracts formed almost simultaneously in a transversal position. Pseudanthial apex is still undifferentiated. (b) Somewhat older developmental stage with four male elements and their subtending bracts formed. Female flower is initiated in pseudanthium center. Note two preceding bracteoles in a median position and a third unpaired prophyll to the left (asterisk). (c) Enlarged male bracts that partially enclose male elements; nectaries are formed between male bracts. Female perianth initiated as four separate primordia (asterisks). (d) Somewhat older developmental stage, two male bracts removed, nectar glands and female perianth are more prominent. (e) Involucre removed, female perianth has begun to bend inward (especially transversal regions), male elements have begun to enlarge. (f) Perianth removed from female flower in (e). Four horseshoe-shaped carpel initials are visible (borders of one highlighted). (g–l) Formation and dedifferentiation of male elements. (g) Young male element with two lateral prophylls (MBl) and central depression (asterisk). (h) Male perianth is in the form of a horseshoe-shaped primordium. (i) Stamen primordium surrounded by ring-shaped primordium. (j) Perianth almost encloses the young stamen. (k) Male inflorescence with a central male flower formed first (1), followed by pairs of male flowers (2+3, 4+5, 6+7), which have formed in rapid succession. (l) View of abaxial side of (k) showing difference in size of flowers 4–5 due to rapid succession of initiation. Bar = 200 μm in a–f; 100 μm in g–l. A, pseudanthial apex; C, carpel; B, bract; Bl, bracteole; F, female flower; M, male element; mb, male bract; MBl, male prophyll; N, nectary; P, perianth; S, stamen.