Study GuidePlant Biology–Seedless Vascular Plants1. Phylum Lycophyta: Club Mosses and More1.1 An Ancient Group of PlantsLycophytes are theoldest living seedless vascular plantson Earth. They belong to one of the twomain evolutionary lines of vascular plants. These two lines split very early—probably during theSilurian Period, and definitely by theDevonian Period.Because of this early split, lycophytes have evolvedindependentlyfrom other vascular plants forabout400 million years. Over time, they changed dramatically. They began as small, semi-aquaticplants and later grew intogiant tree-like formsthat dominated forests during theCoal Agefor nearly40 million years.As continents shifted and climates became drier, lycophytes gradually lost dominance. By the lateCarboniferous to early Permian, most of the large forms became extinct.Interestingly, lycophytes developed features similar to flowering plants, even though they are notclosely related. This is calledconvergent evolution. Traits likeleaves, wood, tree forms, and seed-like reproductive structuresevolved independently in both groups.1.2Lycophytes TodayToday, about1,200 speciesof lycophytes are still alive. They are grouped into three families:•Lycopodiaceae•Selaginellaceae(only one genus:Selaginella, about 700 species)•Isoetaceae(only one genus:Isoetes, about 100 species)Modern lycophytes are much smaller than their ancient relatives. None grow taller than aboutonemeter, even in tropical regions where they are most abundant.Many tropical species areepiphytes, meaning they grow high up in tree canopies. In temperateregions, lycophytes are usuallysmall, creeping, evergreen plants. In the past, people collectedthem to make simple evergreen coverings for graves.SomeSelaginellaspecies are famous as“resurrection plants.”These plants live in very dryenvironments. During droughts, they shut down their metabolism and curl into tight, brown balls thatPreview Mode
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