Warnstorfia Loeske, 1907.

Warnstorfia is becoming more commonly recognized as a segregate of the larger genus Drepanocladus. This latter genus has traditionally been the name for aquatic and pleurocarpous mosses with falcate-secund, narrow leaves and strong costae ending in the leaf acumen. Tuomikoski and Koponen (1979) asserted that Drepanocladus is a phylogenetically diverse grouping that demanded breakup into a number of additional genera. Warnstorfia is distinguished as plants radially (rather than planar) branched with serrulate leaf margins, with a strongly differentiated group of thin-walled and inflated alar cells. The leaf apices have a few somewhat enlarged and seemingly empty cells that function as nematogons. Unlike Drepanocladus sensu stricto, Warnstorfia has the capacity to produce reddish pigmentation in the leaves, especially in sites with strong insolation.
see key to Drepanocladus Etc.

The plants in this section are aquatic pleurocarps, especially in bogs and fens. The plant has a costa that extends into the acumen or beyond, and the leaves are usually falcate-secund.

Species included are all in Campyliaceae:
Warnstorfia exannulata (Bruch & W. P. Schimper) Loeske
Warnstorfia fluitans (Hedwig) Loeske
Warnstorfia pseudostraminea (Müll. Hall.) Tuom. & T. J. Kop., recognized from CA since 2004

Our most common species, Warnstorfia exannulata, is easily confused with Drepanocladus aduncus. Warnstorfia exannulata, when growing in sun and emergent or on mud, tends to have a crimson cast, whereas Drepanocladus aduncus would be only slightly orange. Either could be green though. The alar cells of W. exannulata are larger, like sausages, but both species have large alar cells, so experience is required for use of this character. The two species are also said to have different tendencies as regards pH, with W. exannulata in more acidic conditions.

A. Alar cells inflated and extending in a transversely triangular group nearly or completely across the leaf base; partial hyalodermis distinguishable as a layer of outer cells somewhat larger and thinner walled than adjacent interior ones pseudoparaphyllia often broader than long; plant dioicous .....Warnstorfia exannulata
A. Alar cells restricted to a small pocket in the alar angles, seldom extending to the costa; hyalodermis not distinguishable; pseudoparaphyllia lanceolate; plant autoicous .....Warnstorfia fluitans