Gametophytes, as with all heterosporous plants, develop within the spore wall. Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. However, not all heteromorphic gametophytes come from heterosporous plants. Vascular plants are either homosporous (or isosporous) or heterosporous. Some lycophytes are homosporous while others are heterosporous. The closest relatives of the Marsileaceae are the Salviniaceae, which are also aquatic and heterosporous. However, in most heterosporous plants there are two kinds of sporangia, termed microsporangia and megasporangia. While heterosporous plants produce fewer megaspores, they are significantly larger than their male counterparts. Lycopods are belong to the division Lycopodiophyta, and some are homosporous while others are heterosporous. The seed plants (gymnosperms and angiosperms) are endosporic and heterosporous. It was heterosporous, i.e. the spores were of two distinct sizes. All quillworts and their extinct relatives are heterosporous. If the plant is heterosporous, the sporangia-bearing leaves are distinguished as either microsporophylls or megasporophylls. They included heterosporous water ferns (Salviniales) (placed in a separate subclass by Cronquist et al. All flowering plants are "heterosporous", that is, every individual plant produces two types of spores.