{{Expert needed, biology, talk=Trimorphism#This line seems a misreading of Wallace, reason=Darwin might have misread Wallace, date=December 2018
In
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, trimorphism is the existence in certain
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
s and
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s of three distinct forms, especially in connection with the reproductive organs.
In trimorphic plants there are three forms, differing in the lengths of their
pistils
Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) '' pistils' ...
and stamens, in size and color of their pollen grains, and in some other respects; and, as in each of the three forms there are two sets of stamens, the three forms possess altogether six sets of stamens and three kinds of pistils. These organs are so proportioned in length to each other that half the stamens in two of the forms stand on a level with the stigma of the third form. To obtain full
fertility
Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified demographically. Fertili ...
with these plants, it is necessary that the stigma of the one should be fertilized by pollen taken from the stamens of corresponding height in another form. Hence six unions are legitimate, that is, fully fertile, and 12 are illegitimate, or more or less unfertile. Wallace has shown that the females of certain butterflies from the Malay Archipelago appear in three conspicuously distinct forms without intermediate links.
In crystallography, ''trimorphism'' refers to the occurrence of certain forms in
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
Sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...