Small, Flat, and Featureless- Notothylas orbicularis -An Unusual Hornwort

Please welcome Dr. Bob Klips to Ohio Flora.  Bob writes "Dirty Trees- Bob's Brain on Botany"- without a doubt one of the most interesting sites focusing on plants in the blogsposphere.  Bob has that unusual ability, through his photos and words, to make a tiny plant that he describes as "small, flat, and featureless" incredibly interesting.  

 -Tom 

 An Unusual Hornwort

Notothylas orbicularis

by Dr. Bob Klips 

This promised to be great fun, and it was. A few weeks ago Erik Rothacker, a scientist who studies orchids, invited OSU graduate student Jeff Rose and me to accompany him to see “three birds” orchid at one of his study sites at Dawes Arboretum in Licking County. Seeing the orchid growing right alongside the trail was great, even if it is a mere orchid.

Afterwards we continued hiking through the woods, and saw that the path continued along the edge of the woods bordering a soybean field. Back story: The previous weekend, Jeff and I participated in a bio-blitz where, as usual, that young wippersnapper kept scooping me by spotting cool plants that I had just walked past or even stepped on. Eager to regain a little bot-cred (that’s like “street-cred,” but for bot), I was thrilled to see a wee little moss on the path just where it exited the woods.  Hands-and-knees scrutiny revealed the moss to be one of the exciting short-lived annual mosses generally called “fall ephemerals.” This one, Aphanorrhegma serratum (Funariaceae) turned out not to be a county record, but it is nonetheless fairly uncommon, or at least infrequently noticed. I was pumped! 

Yes, pumped was I, for about two entire minutes. Jeff’s “plant-dar” was set to “high.” He wandered off toward the soybeans and immediately came back holding a little green-topped dirt ball, innocently asking “Can this be this one of those non-Phaeoceros, non-Anthoceros hornworts that have a tiny sideways sporophyte instead of an upright horn-like one?” The answer, which was “yes,” raised another question: How does he do that? The answer to that latter question might involve comparing the visual acuity of someone born during, say, the Reagan Administration compared with someone born during the Truman one. Thank goodness for hand-lenses!

This is a picture of Jeff’s great find, a hornwort called Notothylas orbicularis. Hornworts comprise one of the three plant divisions that are collectively, but informally, referred to as “bryophytes.” The “bryophyte” designation is informal because it is now generally accepted that they do not have an common ancestor that is not also shared with another plant group. The other “bryophyte” divisions are the mosses (Division Bryophyta with just over 400 species in Ohio), and the liverworts (Division Marchantiophyta with approximately 125 species in Ohio.) Hornworts, Division Anthocerotophyta, are a relatively small group that is mainly tropical. Ohio is home to just three hornwort species.

In the photo below, labels have been added, using the font “Comic Sans” that everybody seems to find annoying. They denote the short spindle-shaped sporophytes, laying sideways in characteristic Notothylas fashion. Actually, what we see here are the cylindrical “involucres,” collar-like tubes on the gametophyte within which the sporophytes are developing, and from which they will soon project, but just a bit. See also two mosses: (1) a “fruiting” (sporophyte-producing) individual of the fall ephemeral Aphanorrhegma serratum (big whoop!) and (2) some species of Amblystegiumn. 

Hornworts are awesome. Like all “bryophytes,” (and unlike all other plants) the egg and sperm-producing “gametophyte” stage of the life cycle is the more conspicuous and long-lived of the two life cycle stages. The other stage, the spore-producing “sporophyte,” while genetically distinct from the maternal gametophyte, is permanently attached to the maternal gametophyte that produced it. Hornworts are small, flat, relatively featureless plants that, when lacking sporophytes, are readily mistaken for liverworts. Our hornworts, while infrequently observed, are sometimes abundant and may indeed not be especially rare, but just overlooked. Hornwort habitats are nothing special. Ours are all found on moist disturbed open soil, where they can be almost weedy. They engage in an interesting mutualism, harboring colonies of nitrogen-fixing bacteria within special cavities in their body. 

A hornwort more deserving of the name, and the species that is much more frequently encountered in our region, is Phaeoceros laevis. Here’s a picture of Phaeoceros taken in October a few years ago in Hocking County. Note the spike-like capsules that elongate from the base (a very unusual manner of growth for a plant, as plants usually lengthen only by adding cells at the tip) and split at the end, releasing yellow spores.

Sometimes Phaeoceros grows so densely that it looks like a patch of grass. This specimen was photographed last September in Meigs County.

Bob- Wow, I learned so much.  Thank you for introducing us to the hornworts!
Don't forget to visit "Dirty Trees: Bob's Brain on Botany" for more fantastic botany articles from Bob. 

-Tom

Featured Comment by Dr. Klips-
Late summer and fall are great times to look for hornworts and other "bryophytes." Anyone interested in learning about these plants and meeting a bunch of enthusiastic friendly people eager to share their knowledge about them (and lichens, too!) should look into the Ohio Moss and Lichen Association (OMLA). Information about OMLA, including details of the upcoming Fall Foray to Muskingum County are at www.ohiomosslichen.org.