How to identify Carex

Tired of just writing Carex sp. in reports?

The key to identification of Carex is understanding the unique jargon used in its description. Mastering this small sub set of morphological terminology grants the ability to identify. A majority of the jargon is related to sexually mature flowers that are entirely unisexual - either staminate or pistillate.

Perigynia and achene
Figure 1. a = staminate spike, aa = pistillate spike, b = perigynium,
c = achene

Each female flower develops a modified bract that envelops the ovary for protection and environmental control. These bracts all have a single small terminal opening allowing for fertilization. This 'bag-of-a-bract-with-a-hole-in-the-end' is called a perigynium (singular) or perigynia (plural). After fertilization, the ovary within this perigynium develops into a single nutlet called an achene. Structurally achenes are uniformly either two or three-sided and only possess one of two style types: deciduous or persistent.

Translation: avoid vegetative specimens that lack perigynia and achenes due to immaturity, sterility, or being entirely staminate. These difficult specimens should be given a wide berth until one is familiar with fertile material.

Achene within a perigynium

Perigynia and achenes provide essential diagnostic characters required for the identification and further writing of more than just Carex sp.

Perigynia vary in size, shape, and color

Perigynia diversity

Perigynium size distribution across the genus varies from a couple millimeters long to nearly two centimeters long. They may be flat, round, or trigonous in cross-section.