Biseriate
A botanical term applied to both the Kingdom plantae, and fungi, meaning 'arranged in two rows'.
This can refer to any number of structures within these kingdoms, from arrangement of leaves, to the placement of spores.
This becomes useful in placing a species within a certain genus, family, or even order based upon morphology when making an initial choice, or when DNA (genetic) evidence is inconclusive.
References
http://glossary.gardenweb.com/glossary/biseriate.html
Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Biseriate". Image Credit.