Guide to Hornworts of Oregon: Phymatoceros bulbiculosus (Brot.) Stotler, Doyle, et Crandall-Stotler

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Hornworts 1a stalked tubers present > Phymatoceros bulbiculosus


Synonyms: Anthoceros bulbiculosus Brot.; Anthoceros phymatodes M.A. Howe; Phymatoceros phymatodes (M. Howe) Duff, Villarreal, Cargill, et Renzaglia

Special status: Oregon Biodiversity Information Center List 2 (Threatened), State Rank 1 (Critically Imperiled). USFS Sensitive Species.

Recognition: Solitary chloroplasts in young epidermal cells characterize the family; the smooth thallus with stipitate, ventral tubers distinguish this monotypic genus. Spores are reported to be yellow when young but maturing to fuscous brown or black (Stotler, Doyle, and Crandall-Stotler 2005), smooth or with annular protuberances in the central distal face (Schumacker and Vana 2005). The plants are dioicous, unlike all our other hornworts, with female plants larger than male plants.

Distribution: On seasonally moist, bare mineral soil. Not common; I have seen it in the field only in Curry County where it was abundant at one site in 1979 but not relocated 29 years later despite careful search. Oregon specimens examined: Curry Co.: Harris Wayside, Wagner 1985 (ORE); Rogue River trail between Paradise Bar and Blossom Bar, Stansell s.n. (ORE); Douglas Co.: Bear Creek Recreation Site, Kellman 4330 (CAS); Golden Creek, tributary to Umpqua River near Scottsburg, Sperling B10-JS-03 (DHW).

Comments: Only sterile plants have been found in Oregon. Fortunately, the stipitate tubers are prominent and easily noticed. Regarding the Ethyl Sanborn (1929) records: there are no vouchers at OSC of her citations but there is a single packet which she labeled Anthoceros phymatodes that was collected in 1940. It is Phaeoceros pearsonii, which tells us that she didn't distinguish between the ventral, stalked tubers of Howe's A. phymatodes (=Phymatoceros) and the much more common and widespread Phaeoceros pearsonii which has prominent marginal tubers. I feel justified in dismissing all of the Sanborn literature citations of A. phymatodes.

That I was unable to relocate the Harris Beach population in 2008, despite careful search, demonstrates that this is not a species that can be protected by prohibiting disturbance at a known site along roadsides. Big flushes may occur in recently disturbed sites that expose bare mineral soil. Its adaptability to recently disturbed bare soil shows that it will be pretty much on its own as far as conservation is concerned, occurring on suitable sites that become available as land disturbing activities take place. Under natural conditions it will be found on ledges of cliffs and rock outcrops where erosion keeps bare soil periodically exposed.

A paper by Duff, et al. (2007) provides an argument for recognizing the western North American species as distinct from the European species. They made the combination given above as a synonym. They cite both DNA analysis and anatomy of the chloroplasts to support their opinion. However, Stotler (pers. comm.) has commented that the DNA data they mention are not sufficient to support the species distinction and that the chloroplast distinction is likewise equivocal. For this reason, the species name is here retained as provided in the original description of the genus.


Phymatoceros bulbiculosus, with Targionia hypophylla. Rogue River below Agness, Curry County, Oregon. DHW m2970, field photo.



Phymatoceros bulbiculosus, Golden Creek, Douglas County, OR. Sperling B10-JS-03. Marker indicates thallus lobe turned upside down to show tubers.



Phymatoceros bulbiculosus, Golden Creek, Douglas County, OR. Sperling B10-JS-03.



Phymatoceros bulbiculosus, Coyote Prairie, Lane Co., Oregon. DHW m2716.



Phymatoceros bulbiculosus, chloroplasts. Coyote Prairie, Lane Co., Oregon. DHW m2715.



Phymatoceros bulbiculosus, ventral view showing young, developing stalked tubers, Golden Creek, Douglas County, OR. Sperling B10-JS-03.



Phymatoceros bulbiculosus, nearly mature stalked tubers on living plant. Rogue River below Agness, Curry County, Oregon. DHW m2970, field photo.



Phymatoceros bulbiculosus, dried herbarium specimen, rehydrated and mounted in water, showing mature stalked tubers, Bear Creek Recreation Site, Douglas County, OR. Kellman 4330.



Phymatoceros bulbiculosus, illustration of tubers from Howe, 1899.



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