Cuscuta seeds: Diversity and evolution, value for systematics/identification and exploration of allometric relationships
Fig 2
Summary of character evolution hypotheses.
A. Evolution of epidermis morphology. An invariant epidermis with rectangular, interlocked epidermal cells (Type I) is likely ancestral and characterizes subg. Monogynella. An epidermis with isodiametric cells that can alternate their morphology between dome-shaped and pitted (Type II) evolved in subgenera Cuscuta, Pachystigma and Grammica. B. Evolution of embryo and architecture of palisade layers outside hilum area. The seed coat with only one palisade layer (P1) outside hilum area in subg. Monogynella is likely ancestral, while a seed coat with two palisade layers (P1 and P2) in the remaining subgenera, is likely derived; one palisade layer reverted two times in subg. Grammica in C. microstyla (clade O) and sect. Denticulatae (clade E). The latter taxa also evolved an embryo with an enlarged radicular end, which likely functions as a storage organ. Ep = epidermis; En = endosperm.