Mosses of Central Florida 49. Stereophyllum radiculosum

The flat, dried leaves of  Stereophyllum radiculosum have a
conspicuously bulging midrib.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

Stereophyllum radiculosum (Hooker) Mitten (Stereophyllaceae) forms thin, flat mats on the base of trees, exposed roots, stumps, logs, and limestone,  The distinctive flat leaves are attached uniformly around the stem (not flattened in a plane), elliptic-ovate in shape, and somewhat contorted when dry. The midrib is strong and markedly bulging, but does not reach the tip.  The leaf cells are small, roundish, and contains a single papillum (translucent bump). Spore capsules are erect to somewhat leaning,  asymmetrically egg-shaped, and arise from the bases of the leafy shoot on relatively short stalks (0.6-1.2 mm).

The leaning, egg-shaped spore capsule of Stereophyllum.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

This species is widespread in the tropics; found in the U.S. only in Alabama, Texas, and Florida, where it occurs in the southern part of the state as far north as Citrus, Volusia, and Alachua counties.

Most other creeping species found on tree bases have somewhat flattened shoots, with leaves mainly on two sides of the stem, and capsules strongly bent to the side (Isopterygium or Haplocladium) or symmetrical and upright (Sematophyllum, Entodon).

Mosses of Central Florida 48. Schlotheimia rugifolia

The distinctive brownish shoots of  Schlotheimia rugifolia.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

Schlotheimia rugifolia (Hooker) Schwagrichen (Orthotrichaceae) forms distinctive reddish-brown mats on logs, tree trunks, and branches.  The leafy shoots are more or less erect (extending away from attached base).  The flat leaves twist spirally around the stem when dry.

The narrow-ovoid capsules are usually erect, but bent in this
dry specimen. Photo by Juan David Parra copyright MBG,
posted on Tropicos,  available under a Creative Commons
License.

The leaves  of this species are elliptic, with short point at tip and have a slight rumpled (rugose) appearance. The midrib is strong, extending through to the short point.  Leaf cells are small, roundish, and smooth.  The spore capsules are erect and narrow-ovate in shape. They arise from the tips of the leafy shoots on elongate stalks,
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Schlotheimia rugifolia  is found throughout the southeastern U.S. as far north as Virginia and Tennessee, and extensively in the New World tropics.  In Florida, it has been collected throughout the state but with gaps.  In particular, it has not been collected in any of the Atlantic coastal counties between Volusia and Miami-Dade.

This is one of the relatively few mosses found in Florida that occur relatively high on the trunks and branches of trees.  The dark, reddish brown coloring, the distinctive spiral twisting of the dried leaves and the longer capsule stalks will distinguish it from others, such as Sematophyllum,  Cryphaea, and Forsstroemia, in this habitat.

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Mosses of Central Florida 47. Aulocomnium palustre

Aulacomnium palustre (Hedwig) Schwagrichen (Aulacomniaceae) forms tufted colonies of upright leafy shoots on wet soil, marshes, swamps, and sometimes rocks.  It employs asexual propagation via small, modified, bullet-shaped or spear-point leaves clustered at the tips of elongate stems.

The upright shoots of Aulacomnium palustre form loose tufts
on wet soil. Photo by Robert A. Klips.

The leaves are elongate, with a prominent midrib, and gradually come to a point.  Leaf cells are small, roundish and papillose.  Spore capsules are bent to the side, and distinctly grooved, but are not commonly seen in our area, as asexual propagation is abundant.

A single tapered leaf of Aulacomnium palustre, showing
the prominent midrib and tiny, rounded cells.
Photo courtesy Western New Mexico Herbarium,
from the Gila Wilderness.

This species is found in every state and province of North America and throughout the northern hemisphere.  In Florida it has been collected in scattered counties in the northern half of the state, as far south as Polk County.

Mosses of Central florida 46. The genus Leskea

Leskea gracilescens growing on the side of a tree.  Photo by
Robert A Klips

Three of the four species of  Leskea found in North America have been reported from Florida: Leskea australis Sharp,  L. gracilescens Hedwig, and L. obscura Hedwig.   These are creeping, irregularly branched, mat-forming mosses, often with a reddish coloration, found on the bases or lower trunks of hardwoods and cypress trees, or on decaying logs. 

A leaf of Leskea gracilescens, showing the small roundish
cells with papillae (translucent light spots).  Photo by Kalman
Strauss, posted in the Consortium of North American
Bryophyte Herbaria database.

Leaves are ovate and pointed, with midribs that usually end before the tip.  Leaf cells are small, roundish, and papillose, and the spore capsules are erect and more-or-less symmetrical.

Only Leskea australis is known from central Florida.  It has been found throughout the state, but has not been reported from the extreme south, the western panhandle or the Atlantic coastal counties. Elsewhere, it is found throughout the southeastern U.S.

A leafy shoot of Leskea gracilescens with an inset of the
papillose leaf cells.  Photo by Robert A.Klips

The erect, symmetrical spore capsules of Leskea gracilescens.
Photo by Kalman Strauss.

L. gracilescens and L. obscura are both widely distributed in eastern North America, live in the same habitats as L. australis, and differ in minor ways. L. grascilescens has been reported from several counties in North Florida, elsewhere throughout eastern North America, and L. obscura only from Leon County.

Our Leskea species are similar to Haplocladium microphyllum, also in the Leskeaceae, but in Haplocladium the spore capsules are bent distincly to the side, and the leaf tips more drawn out into a narrow point.  H. microphyllum is also more likely found in soil, rocks or damp wood than on tree trunks. 

Pond edges, liverworts, and the earliest land plants

.The edge of a drying pond would hardly seem like a hospitable place for plant life.  During the wet season it is submerged, and during the dry season it can be completely dried out.  Yet for the few months when the shoreline is retreating, during winter and spring in Florida, the sandy soil between high and low water marks remains moist, and supports a variety of small, but quick-growing plants that complete their life cycles before being inundated again.

Some green plants can be seen along this drying pond edge, but
the most interesting residents can only be seen close-up.

I have previously reported on some ephemeral inhabitants of such pond edges, including the sundew, Drosera capillaris, and several mosses, including Rosulabryum capillare,  Physcomitrium collenchymum, and some species of Micromitrium.  I expect to report on several other mosses with similar habits in the coming months.
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Recently, I was out walking in my neighborhood, and decided to revisit the same pond edge where I had collected Physcomitrium collenchymum in late March a couple of years ago. Now, in late January, I was quite surprised to find two completely different bryophytes,  Riccia cavernosa, and a species of Sphaerocarpos - both liverworts - but no sign of the Physcomitrium.  I shall have to pay attention over the next several months, to see if there is a succession of different species that might include later appearances of a  moss or two.

Riccia forms a flat, forking thallus, while Sphaerocarpos takes the form of a rounded mound of upright shoots.

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Riccia cavernosa is a thallose liverwort, meaning its body is in the form of a flattened, forking ribbon. Riccia species tend to spread outward from a central point, forming a round disk, at least when young, One can see here that the thallus is heavily pitted, giving it a spongy texture.

Sphaerocarpos species form cushions of odd egg-shaped shoots.

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.Finding these liverworts got me to thinking again about the very first land plants, which  most likely lived in a similar habitat, and were similar in growth forms to modern thallose liverwort like Riccia.  Phylogenetic studies indicate that the closest living relatives of land plants are in the green algal genus Coleochaete, which has a similar flat, disk-like growth form.  So it is easy to see an ancient transition from one to the other.

The green alga, Coleochaete, grows as
a flat sheet of tissue (A,B) that expands
outward from its center. The roundish
bodies are zygotes, that will eventually
undergo meiosis to produce zoospores (C).
from Essig 2015, after Haupt.

To be sure, some major adaptive innovations took place as green algae moved onto land, especially in their mode of reproduction. Coleochaete, like other green algae, produces zoospores through meiosis of the zygote, while all bryophytes have a diploid sporophyte generation that produces non-motile, dessication-resistant spores through meiosis of cells within a spore chamber or capsule.

[several interesting copyrighted photos of Coleochaete species can be seen at The Vine Tendril , and The Algal Web.

Also to be sure, Riccia is a modern liverwort genus, and I don't suggest that the first land plant were members of that genus that have been sitting around unchanged for 400 million years.  Most likely the ancestors of Riccia readapted to this habitat, as many others have over the ages, including the Sphaerocarpos, various mosses, and certainly the Drosera.

Part of that readaptation, is a shift back to the means of spore dispersal most likely practiced by the first land plants. In most bryophytes, the spore capsule is elevated by a stalk to facilitate wind-dispersal. The spore chamber of Riccia  is however very simple and lacks a stalk. It remains embedded within the thallus until the latter disintegrates, and the spores are then dispersed by water currents as the pond level rises, or on the feet of birds walking around in the mud.  Seeds of Drosera capillaris are probably dispersed in a similar way.

The sporophyte of Riccia is embedded within the gametophyte
thallus.  It consists of a thin wall (the capsule) containing a mass
of diploid tissue, which here has been transformed through
meiotic division into a number of hard-walled spores. From
Essig 2015, after Brown.

So the water-edge habitat has continued to host a dynamic community of ephemeral plants of similar growth form and reproductive habits since the very first colonization of the land.

Reference:
Essig, Frederick B., 2015. Plant Life - a Brief History. Oxford University Press.

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