monomorfen

Monomorfen is a term used in biology to describe organisms or populations that display a single morphological form across life stages and sexes. Unlike polymorphic taxa, which exhibit distinct alternative forms, monomorfen are characterized by uniform external morphology, even if other traits such as behavior or life history differ.

Etymology and usage: The term combines Greek monos meaning "one" and morph meaning "form." It has appeared in various taxonomic and ecological texts since the early 20th century, though its usage is not universal and some authors prefer related terms such as monomorphy or monoform.

Characteristics: The key feature is constancy of external form. In practice, some polyphenic or phenotypically plastic species may still be considered monomorfen if the observed individuals share the same phenotype under common conditions. The concept is closely linked with discussions of phenotypic plasticity, cryptic diversity, and the challenges of identifying polymorphism in field studies.

Distribution and examples: Because monomorphism can occur in both animals and plants, it is reported in diverse groups, but robust classifications are limited by sampling. Researchers assess morphology using measurements, imaging, and sometimes genetic data to determine whether variation is genetic or environmental.

See also: polymorphism, dimorphism, phenotypic plasticity, cryptic species, monomorphism (biology).