asexual
sporophyte generation) In
mosses,
liverworts and
hornworts, an unbranched
sporophyte produces a single sporangium, which may be quite complex morphologically. Most non-vascular plants, as well as many
lycophytes and most ferns, are
homosporous (only one kind of spore is produced). Some lycophytes, such as the
Selaginellaceae and
Isoetaceae, the extinct
Lepidodendrales, and ferns, such as the
Marsileaceae and
Salviniaceae are
heterosporous (two kinds of spores are produced). These plants produce both
microspores and
megaspores, which give rise to gametophytes that are functionally male or female, respectively. Most heterosporous plants there are two kinds of sporangia, termed
microsporangia and megasporangia. leaf ''
strobilus cut open to reveal sporangia Sporangia can be terminal (on the tips) or lateral (placed along the side) of stems or associated with leaves. In
ferns, sporangia are typically found on the
abaxial surface (underside) of the leaf and are densely aggregated into clusters called
sori. Sori may be covered by a structure called an indusium. Some ferns have their sporangia scattered along reduced leaf segments or along (or just in from) the margin of the leaf. Lycophytes, in contrast, bear their sporangia on the
adaxial surface (the upper side) of leaves or laterally on stems. Leaves that bear sporangia are called
sporophylls. If the plant is heterosporous, the sporangia-bearing leaves are distinguished as either microsporophylls or megasporophylls. In seed plants, sporangia are typically located within
strobili or flowers.
Cycads form their microsporangia on microsporophylls which are aggregated into strobili. Megasporangia are formed into ovules, which are borne on megasporophylls, which are aggregated into strobili on separate plants (all cycads are dioecious).
Conifers typically bear their microsporangia on microsporophylls aggregated into papery pollen strobili, and the ovules, are located on modified stem axes forming compound ovuliferous cone scales. Flowering plants contain microsporangia in the anthers of
stamens (typically four microsporangia per anther) and megasporangia inside
ovules inside ovaries. In all seed plants, spores are produced by meiosis and develop into gametophytes while still inside the sporangium. The microspores become microgametophytes (pollen). The megaspores become megagametophytes (embryo sacs).
Eusporangia and leptosporangia Categorized based on developmental sequence,
eusporangia and
leptosporangia are differentiated in the vascular plants. • In a leptosporangium, found only in leptosporangiate ferns, development involves a single initial cell that becomes the stalk, wall, and spores within the sporangium. There are around 64 spores in a leptosporangium. of fern leptosporangia • In a eusporangium, characteristic of all other vascular plants and some primitive ferns, the initials are in a layer (i.e., more than one). A eusporangium is larger (hence contain more spores), and its wall is multi-layered. Although the wall may be stretched and damaged, resulting in only one cell-layer remaining.
Synangium A cluster of sporangia that have become fused in development is called a
synangium (pl.
synangia). This structure is most prominent in
Psilotum and
Marattiaceae such as
Christensenia,
Danaea and
Marattia. ==Internal structures==