Fig. 4.

Meristems and developmental pathways. The combination of different meristem types and developmental pathways allows the deduction of all forms of flowering shoot systems (see Figs 5 and 6). (A) Tip of a shoot system with vegetative meristems (green) in terminal and axillary position. (B) Transition to reproductive meristems (dark red), (B₁) at axillary positions (white arrow: acropetal development), (B₂) terminal and axillary position, (B₃) terminal position, (B₄) terminal position followed by induced axillary meristems (white arrow: basipetal sequence); (C) early reproductive meristem with indeterminate tip (light green zone), (C₁) producing lateral partial inflorescences (compound inflorescences), (C₂) producing lateral flowers or floral units (simple inflorescences). (D) Tip of late reproductive meristem, (D₁) remaining indeterminate (cross) and rarely returning to vegetative growth (grey dashed line), (D₂) merging into the determinate stage (light red; terminal flower/FU). (E) Determinate reproductive meristem (red) originating a floral unit (E_1–6: red–yellow grade) or flower (E₀: yellow). Grey frames: meristems and meristem parts exemplarily illustrating possible developmental pathways; arrows: developmental alternatives; green–red colour gradient: increasing reproductive signals in inflorescence meristems; red–yellow colour gradient: floral unit meristem fractionating into sub-meristems before starting flower production.