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General. Tetrads

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A general term for a group of four united pollen grains or spores, either as a dispersal unit or as a developmental stage.
Decussate tetrad
A multiplanar tetrad of pollen grains or spores arranged in two pairs lying across one another, the pairs (dyads) more or less at right angles to each other. Example: Orophea(Annonaceae).
Cross tetrad
Synonym of decussate tetrad.
Anisodiametric tetrad
General term for tetrads which members are differing in size. Example: seed-megasporetetrads.
General term for two microspores (pollen grains or spores) united as a dispersal unit.
Isodiametric tetrad
A general term for tetrads in which all members are more or less the same in size.
Linear tetrad
A uniplanar tetrad in which the four members are arranged in a row. Example: Typhaspp. (Typhaceae).
Multiplanar tetrad
A tetrad in which the individual members are arranged in more than one plane.
Rhomboidal tetrad
A uniplanar tetrad in which the proximal faces of two individual members are in direct contact and the remaining two are separated, giving a rhomboidal outline to the tetrad. Example: Epipactis palustris (Orchidaceae).
S-type tetrad
A tetrad in which only one members is fully developed. Example: Leucopogon fasciculatus (Epacridaceae).
Square tetrad
Synonym of tetragonal tetrad.
Tetragonal tetrad
A uniplanar tetrad in which all four members are in contact at the centre of the tetrad so that, in the correct orientation, the adjacent walls form a cross. Example: Uvariastrum hexaloboides (Annonaceae)
Tetrahedral tetrad
A multiplanar tetrad in which each member is in contact with three others, so that the centers of the grains define a tetrahedron. Example: Erica (Ericaceae).
Describing tetrads or polyads in which the sexine/ectexine of each monad is well differentiated, but does not form a single continuous envelope around the unit. Example:Drosera (Droseraceae).
Uniplanar tetrad
A tetrad in which the individual members lie more or less in one plane.