Early fossil records of endospory have not been discussed in literature, but the oldest extant lineage with heterospory, the Selaginella, have been recognized as a potential intermediate in the morphological evolution to endospory due to its megaspores' potential for photosynthesis and rhizoids extending from the trilete structure.
[6] Endosporic megagametophytes extend only rhizoids and the archegonium from the spore wall, they often lack chlorophyll,[1] and they do not acquire nutrients from the soil.
[1][5] The retention of gametophytes within the spore wall additionally provided advantages for selection in ecological settings after fertilization.
The support provided by the spore wall, which is similar but not as advanced as an ovule, increased reproductive success allowing for strong selective advantages during competition.
[1] The development of gametophytes within spore walls provided improvements in sexual function as well as protection from harsh conditions.