Fissidens fontanus, Nomencl. Bot. Plant. Crypt. 166. 1824. -- Skitophyllum fontanum B.-Pyl., J. Bot. (Paris) 2, 4(4): 158. 1814. -- Octodiceras fontanum (B.-Pyl.) Lindb. Oefv. K. Svensk. Vet. Akad. Foerh. 20: 405. 1863. -- Fontinalis juliana Savi ex DC., Fl. Franc., ed. 3, 6: 236. 1815. -- Fissidens julianus (Savi ex DC.) Schimp., Flora 21: 271. 1838. -- Octodiceras julianum (avi ex DC.) Brid., Bryol. Univ. 2: 678. 1827. -- Fissidens debilis Schwaegr., Spec. Musc. Suppl. 1(2): 11. 1816.

   Plants flaccid, dark green to yellowish green, bleaching almost to white, to 6 cm high, mostly with more than 10 pairs of leaves, irregularly crinkled when dry. Leaves distantly inserted except near stem apex, spreading from stem at about a 45 degree angle, to 6 mm long, linear lanceolate to linear, more than 10: 1, bluntly acute to acute at apex. Vaginant lamina about 8: 1, mostly extending 1/4 to 1/3 of leaf, with the two sides equal. Dorsal lamina tapered at base, mostly not extending to leaf insertion. Median cells of all laminae unistratose, smooth on both surfaces, to 12 µm wide, hexagonal with angular lumens and rather thin walls. Juxtacostal median cells markedly larger than adjacent median cells; median marginal cells markedly smaller. Costa to 60 µm broad at base, tapering only near its apex, ending within about 5–10 cells of leaf apex. Margin not at all decurrent, unistratose and plane, regularly crenulate. Costa cross-section of 4–5 layers of thin-walled to substereidal cells, nearly homogeneous except for size differentiation. Stem without central strand, with rather thin-walled inner cortical cells and with 1–2 poorly differentiated layers of smaller, red-brown and somewhat thick-walled outer corticals. Axillary hyaline nodules not present.

   Autoicous with perigonia axillary, and with the perichaetia on short axillary branchlets. Seta to 10 mm, erect above its deflexed base. Urn to 0.6 mm long, cylindric and symmetrical. Operculum rostrate, about as long as urn. Annulus present and persistent. Exothecial cells to 12 µm wide, short rectangular, to 2.5: 1, in very regular rows, isodiametric and smaller near mouth, rather thick walled with lumen: wall ratio about 4: 1. Peristome papillose to papillose striate near the base, spirally ridged distally, deeply but irregularly bi- to tri-fid. Spores to 20 µm, coarsely papillose.

   This is one of the most distinctive Fissidens in California. No other local plant in the genus has such long and narrow, very flaccid leaves without a limbidium. On this basis, and because of the irregularly divided peristome teeth, many bryologists such as Smith (1978) place it in the segregate genus Octodiceras. With some hesitation I have rejected that option. The several species which are often assigned to Octodiceras are the subject of an excellent world monograph by Pursell (1988). My records show this to be an extremely rare plant in California, but many of its best habitats were probably destroyed in the early cultivation of the Central Valley of California. My records are limited to the Napa Valley, Napa County, and to the margins of Clear Lake, Lake County. It should be looked for in any calcareous, shallow and sluggishly flowing water at low elevations. It may easily be overlooked as it may be heavily overgrown by filamentous algae in the highly mineralized water in which it so often grows.

Vouchers: Kern Co.: Kern River along Highway 178 near Richbar, Sequoia National Forest, Shevock 12883 & 16763 (confirmed by Pursell) and outlet of Lake Isabella, Laeger 528 (CAS, PAC, UC); Lake Co.: South shore Clear Lake at Corinthian Bay County Park, Norris 71780, City of Clear Lake Public Pier, Toren 6845 (CAS), Clear Lake State Park, Toren 6846 (CAS) east shore of Blue Lakes, Toren 523 (SFSU), and Rodman Slough near Upper Lake, Shevock & Toren 20306; Marin Co.: Lily Lake, Toren 963 (SFSU); Napa Co.: Weeks Ranch about 3 miles from Calistoga towards Petrified Forest, Koch 1397 (UC); Santa Cruz Co.: Quail Hollow Pond, Quail Hollow Ranch County Park, Kellman 2613 (CAS).

Literature: Crum and Anderson 1981; Kellman 2003; Lawton 1971; Toren 1977; Yurky 1990, 1995. As Octodiceras fontanum Koch 1950a. As Octodiceras julianum Britton 1902.

Illustration References: Malcolm et al. 2009 p. 85; Crum and Anderson 1981; Ignatov and Ignatova 2003; Koponen et al. 1995; Lawton 1971; Pursell 1987; Sharp et al. 1994; Smith 1978.

Elevation by latitude plot for Fissidens fontanus
   in California