Figure 1: Cladogram displaying independent losses of motile sperm during plant evolution and Physcomitrella patens sexual life cycle.

(a): The LECA (last eukaryotic common ancestor) gave rise to eukaryotes of all five kingdoms, in which Archaeplastida harbour the green lineage. Zygnematophyceae, Coleochaetophyceae and Charophyceae (ZCC grade) are sister to land plants (One Thousand Plant Transcriptomes, 2019). Bryophytes are probably monophyletic (see text for references) comprise hornworts, liverworts and mosses, and are sister to vascular plants. Flagella were present in the LECA and were lost three times independently during plant evolution (red cross indicates absence of flagella). Drawn based on DeVries and Archibald 2018, Mast et al., 2014, Puttick et al., 2018.

(b): Upon environmental stimulus, reproductive organs (gametangia) develop on the apex of each gametophore, namely archegonia (female) and antheridia (male). Additionally, paraphyses emerge (p). Mature antheridia release the motile (flagellated) spermatozoids upon watering. The sperm cells swim through the archegonial venter to fertilize the egg cell. After fertilization, embryo development (E1/E2) and sporophyte development (ES-B) occurs. The mature sporophyte is located on the apex of the gametophore and releases haploid spores of the next generation. P. patens is predominantly selfing. Embryo/sporophyte developmental stages according to Hiss et al. (2017).