Complex sentence: Annals of Botany doi: 10.1093/aob/mct033 When a moss spore germinates it grows to produce a filament of cells (called the protonema).
Split into simpler sentences: Annals of Botany doi: 10.1093/aob/mct033 Moss gametophytes originate from the germination of a spore. The initial phase of growth leads to a filament of cells (called the protonema).