Types in flowering plants Apomixis

caribbean agave producing plantlets on old flower stem.

maheshwari used following simple classification of types of apomixis in flowering plants:

nonrecurrent apomixis: in type megaspore mother cell undergoes usual meiotic divisions , haploid embryo sac [megagametophyte] formed. new embryo may arise either egg (haploid parthenogenesis) or other cell of gametophyte (haploid apogamy). haploid plants have half many chromosomes mother plant, , process not repeated 1 generation (which why called nonrecurrent). see parthenogenesis , apogamy below.
recurrent apomixis, more called gametophytic apomixis: in type, megagametophyte has same number of chromosomes mother plant because meiosis not completed. arises either archesporial cell or other part of nucellus.
adventive embryony, called sporophytic apomixis, sporophytic budding, or nucellar embryony: here there may megagametophyte in ovule, embryos not arise cells of gametophyte; arise cells of nucellus or integument. adventive embryony important in several species of citrus, in garcinia, euphorbia dulcis, mangifera indica etc.
vegetative apomixis: in type flowers replaced bulbils or other vegetative propagules germinate while still on plant . vegetative apomixis important in allium, fragaria, agave, , grasses, among others.

types of gametophytic apomixis

gametophytic apomixis in flowering plants develops in several different ways. megagametophyte develops egg cell within develops embryo through parthenogenesis. central cell of megagametophyte may require fertilization form endosperm, pseudogamous gametophytic apomixis, or in autonomous gametophytic apomixis fertilization not required.

in diplospory (also called generative apospory), megagametophyte arises cell of archesporium.
in apospory (also called somatic apospory), megagametophyte arises other nucellus cell.

considerable confusion has resulted because diplospory defined involve megaspore mother cell only, number of plant families have multicellular archesporium , megagametophyte originate archesporium cell.

diplospory further subdivided according how megagametophyte forms:

allium odorum–a. nutans type. chromosomes double (endomitosis) , meiosis proceeds in unusual way, chromosome copies pairing (rather original maternal , paternal copies pairing up).
taraxacum type: meiosis fails complete, meiosis ii creates 2 cells, 1 of degenerates; 3 mitotic divisions form megagametophyte.
ixeris type: meiosis fails complete; 3 rounds of nuclear division occur without cell-wall formation; wall formation occurs.
blumea–elymus types: mitotic division followed degeneration of 1 cell; 3 mitotic divisions form megagametophyte.
antennaria–hieracium types: 3 mitotic divisions form megagametophyte.
eragrostis–panicum types: 2 mitotic division give 4-nucleate megagametophyte, cell walls form either 3 or 4 cells.




^ cite error: named reference maheshwari invoked never defined (see page).
^ nogler, g.a. 1984. gametophytic apomixis. in embryology of angiosperms. edited b.m. johri. springer, berlin, germany. pp. 475–518.