Liverworts and mosses were once placed in the phylum (division) Bryophyta (bryophytes), embryo-producing plants (embryophytes) without a water conducting system (nonvascular). As a young student in a botany class at Arcadia High School, I was very fond of liverworts and there was a nice population of Marchantia on the shady, north side of our biology lab room. DNA research has resulted in a detailed evolutionary tree for the plant kingdom. The primitive nonvascular bryophytes represent three clades (branches) or offshoots from the base of the tree that are often treated as divisions: Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerotophyta (hornworts). Hornworts are especially interesting because they greatly resemble some of the earliest land plants on Earth. The Marchantiophyta include thalloid liverworts (class Marchantiopsida) with a plant body called a thallus. Leafy liverworts belong to class Jungermanniopsida.

Cladistic analyses suggest that the hornworts (Anthocerotophyta) originated much earlier in the history of land plants, possibly before the Devonian. Fossil bryophytes are scarce, but some bryophyte-like fossils have been found in Carboniferous deposits (300 million years ago) and older. Hornworts may even be one of the earliest lineages of land plants. Some of their morphological characteristics are similar to sporophytes of the ancient land plant Horneophyton that lacked true vascular tissue. In fact, some paleobotanists have suggested that Horneophyton may be the "missing link" between hornworts and the Rhyniopsida, an extinct class of early vascular plants. Fossils of these ancient land plants are well represented in the early Devonian Rhynie Chert beds in Aberdeenshire in the north of Scotland. This time period is approximately 398-416 million years ago, long before the age of dinosaurs. Hornworts are certainly one of the most unusual and fascinating plant groups on earth. On a road trip from Banning to Idyllwild I once stopped at a roadside seepage area and, lo and behold, I found a population of hornworts!

Botanist Beth Pearson & her student Isabelle Massaro also discovered bottleworts (Sphaerocarpos) in the Arboretum. Bottleworts are in the thalloid liverwort class Marchantiopsida with a plant body called a thallus. The erect bottle-like structures (involucres) with an opening at tip surround the female sex organs (archegonia) and the spore-bearing capsule (sporangium) after fertilization.

The following reference separates the four California species of Sphaerocarpos by their spores. Spores of S. drewiae remain united in tetrads after capsule dehiscence. The tetrads are lamellate with parallel ridges. S. michelii and S. texanus have areolate spore tetrads. Spores of S. cristatus are smaller and separate long before capsule maturity. I originally thought we had S. cristatus and S. texanus in the Arboretum; however, I now believe that my S. cristatus conclusion was premature and incorrect. The sporangia I examined in early February were immature (transparent, wet & slimy) and tetrads may not have formed yet. In fact, I may have been photographing spore mother cells (sporocytes) prior to meiosis. The sporangia I observed in late February contained distinct, dark brown or black tetrads under 400x magnification with a compound microscope.

As of 29 February I was not positive on my identification of Sphaerocarpos texanus. The spores were clearly released from sporangia in tetrads, but without an scanning electron microscope I just couldn't see detail of the spore surface. I finally examined a sample of dark spore tetrads with a compound microscope with a bright light above the stage. Low & behold there were parallel ridges on spore surface! This has to be the rare & endangered bottlewort Sphaerocarpos drewiae (also spelled S. drewei) endemic to California. It has a California Native Plant Society rating of 1B.1: Seriously endangered in California due primarily to habitat destruction. NatureServe Explorer rates this species as G1 Critically Imperiled. Their next higher rating is "Possibly Extinct." This discovery should be documented for the Palomar College Arboretum. It is possible that a second species of Sphaerocarpos occurs in the Arboretum area; however, I believe that the different initial names I came up with were premature conclusions based on images of different stages of spore development from the same species.

The bottlewort (Sphaerocarpos texanus) appears on a stamp in the country of Montenegro in southern-southeastern Europe. Montenegro is a Balkan country with rugged mountains, medieval villages and a narrow strip of beaches along its Adriatic coastline. Sphaerocarpos texanus has a worldwide distribution. In fact, it also occurs in California, including San Diego County.

Frillworts are small, delicate leafy liverwort species growing on moist soils throughout our planet, from subarctic to subantarctic and on all major continents. Under a dissecting microscope the leaves appear like clothing frill, defined as gathered, pleated, or bias-cut fabric edging used on dresses and blouses. Some types of lettuce also have leaves that appear frilled. The name frillwort: is derived from "Frill" + "Wort" (old English word for plant). The best way to describe the appearance of frillwort leaves is with the following image comparing clothing frill with frillwort plant in Palomar College Arboretum.

Using 100x oil immersion objective (1000x magnification) and focusing up & down due to limited depth of field, I can barely count the lamellae at circumference of spore. I cannot even come close to the number range (30-44) described by Doyle & Stotler (2006) for Fossombronia longisecta. F. pusilla has 11-28 lamellae (layers) and my count is at least a dozen lamellae. It is possible that my equipment (and microscope skills) are not up to par for this critical observation; however, I stand by my determination of F. pusilla for the Palomar College Arboretum. In addition, F. pusilla is listed for San Diego County by Doyle & Stotler (2006). Note: This image uprezzed with Photoshop plugin Genuine Fractals.

Thallose liverworts cannot control their water loss (transpiration) through the pores. Without a water conducting system of cells (vascular tissue) and without pores (stomata) controlled by guard cells, they typically live in shady, moist areas where they can imbibe water, and where there is sufficient water for their swimming sperm to reach the egg. However, there is now evidence that minute arthropods (collembolans & mites) may passively facilitate the transfer of sperm in mosses. As I stated above, frillworts (Fossombronia) can survive in relatively dry areas during summer and fall by the production of underground tubers. Magnification 400x.

Moss Fertilization By Microscopic Springtails   Thallose Liverwort In Creek Near Walker River

Without Water-Conducting Cells, Nonvascular Plants Must Be Small Like Liverworts

Left: Vessels from Brodiaea terrestris ssp. kernensis, a rare flowering plant in the vernal pool field near Palomar College. The spirally-thickened secondary cell walls appear like coiled springs. This provides strength as well as flexibility to these strands of tubular, water-conducting cells that compose the xylem (vascular) tissue. Right: Two types of water-conducting cells: tracheid and vessel (vessel element). Technically a vessel is composed of many hollow vessel elements joined end-to-end like sections of PVC pipe. Vessels are characteristic of all flowering plants, except for the earliest ancestral sister clade (Amborella) that have only tracheids like most gymnosperms.

Without Guard Cells, Liverworts Cannot Control Water Loss Through Their Pores. They Typically Live In Moist Places Microscopic view of the paired guard cells and stoma on the leaf surface of a flowering plant (Tradescantia). An opening or stoma develops between the inflated (turgid) guard cells due to a differential thickening of their walls. When the guard cells lose water pressure on a hot day, they deflate and push together, thus closing off the stoma and reducing water loss (transpiration) through the leaf. During January 2020 liverworts were abundant in the Palomar College Arboretum in exposed areas with full sun. This is due to substantial rains in December 2019 producing moist soils conducive to spore germination. I might add that frillworts (Fossombronia) can survive in relatively dry areas during summer and fall by the production of underground tubers.

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Orobus-Seed Liverwort (Targionia hypophylla) in Twin Oaks Valley

The British Bryological Society describes a liverwort species quite unlike other species of liverworts. It has shiny black, bivalved, female involucres at the apex of leaves. The involucre contains egg-bearing archegonium. After fertilization, a sporangium develops within involucre. The spore capsule has been described as resembling a miniature mussel shell! I discovered this species growing on a moss & lichen-covered bank at a cul-de-sac in Twin Oaks Valley east of Owens Peak. This unique species of liverwort has a remarkable worldwide distribution. Orobus is a former genus of European perennial herbs in the legume family (Fabaceae), some of which were replaced by Lathyrus (sweet pea). It is also the specific epithet for a species of bitter vetch (Vicia orobus)

British Bryological Society Page About Targionia

In addition to the liverwort Targionia, this lichen & moss-covered embankment also contained several frillworts (Fossombronia).

Colony of strap-shaped Targionia with prominent air pores on upper side of leaf-like thallus. Some "leaves" have black, female involucre at their tips.).

Magnified view of shiny black, bivalve female involucre at tip of "leaf." After fertilization of egg inside the archegonium, the zygote develops into diploid sporangium. This image shows the involucre separating into the 2 valves and releasing spores from the multispore sporangium. This was a difficult photo to capture.

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Desert Cryptobiotic Crust

Bryophytes and lichens are important components of desert cryptobiotic soil crust and we have some of these in the Palomar College Arboretum and adjacent coastal sage scrub. In fact, one is a white soil lichen near the bottlewort population on upper Arboretum trail. See following reference:

A Field Guide To Biological Soil Crusts Of Western U.S. Drylands: Common Lichens & Bryophytes by Roger Rosentreter, Matthew Bowker, & Jayne Belnap. 2007. U.S. Geological Survey   Field Guide To Cryptobiotic Soil Crusts In The Western United States

This is a thin whitish lichen crust with granular (powdery) soredia and few fungal apothecia. It appears after winter rains and often disappears during the dry weather of late spring and summer. It may be in the genus Trapeliopsis, possibly T. granulosa.

Microscopic view of soredia from the granular (powdery) surface of Trapeliopsis, possibly T. granulosa. Each soredium contains several green algal cells enveloped by filamentous fungal hyphae. Like dust particles, the soredia are carried by the wind to different locations where they develop into new lichens. The upper surface of lichen thallus is covered with these minute soredia. This is how many lichen species spread to new locations. Why start from a fungal spore from an apothecium when you already have both symbionts in soredium: the photobiont (alga) and mycobiont (fungus). A fungal spore must land on suitable substrate and hopefully encounter its algal mate. Lichens are truly a "marriage" between algae and fungi. I once worked with a student at Cal State University San Marcos who grew the algal & fungal components of the lichen "British soldiers" separately (see following link). British soldiers (Cladonia cristatella), is an attractive soil lichen with upright podetia bearing bright red apothecia at the tips. The fungus appeared like an amorphous blob of tissue while the algae appeared as bright green cells. Only in the combined lichen state does the true body form appear. This is an excellent example of synergism where the whole is truly greater than the sum of its parts. Using gel electrophoresis, the lichen DNA clearly showed gene activity not present in the symbionts.   Symbiogenesis: British Soldiers

Arid desert regions throughout the world where vegetation is sparse sometimes develop specialized communities of cyanobacteria, mosses, liverworts, and lichens. The surface soil is held together by these associations called "cryptobiotic soil crusts." These crusts are very fragile and are easily damaged by walking on them. After sufficient rains, some of the small nonvascular plants and lichens turn greenish. Even when dry they form a protective crust layer. Cryptobiotic crusts are very beneficial because they hold soils in place and protect the underlying sediments from erosion. They are also an important pioneer stage in succession on bare ground (xerarch succession), thus enabling grasses and herbs to become established. In fact, the above lichen (Trapeliopsis) has been dissiminated in recently burned forests of Quebec.

Another White Crustose Soil Lichen In The Arboretum & On Owens Peak

Cryptobiotic Crust In Anza-Borrego Desert

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Primitive Vascular Worts In The San Marcos Area!

Horsetails (Equisetum hyemale), a primitive vascular plant (pteridophyte) with jointed stems and a terminal spore cone (strobilus). Because this genus dates back to the Carboniferous era (300 million years ago), it is sometimes called a "living fossil." They are also called "scouring rushes" because the silica-impregnated stems were used to clean pots and pans. The sporangia within the strobilus also contain hygroscopic elaters similar to some bryophytes.

I probably should mention two more interesting, primitive vascular worts (pteridophytes) in a vernal pool field near the William R. Bradley Park: Pillworts (Pillularia) and quillworts (Isoetes). When I majored in botany at California State University, Los Angeles I only saw these plants preserved in jars or pressed and dried on herbarium sheets. Unfortunately, the field is for sale and the vernal pools, several federally endangered plants and the San Diego fairy shrimp are threatened due to land developers in this pro-growth area. Some of these plants also occur in a nearby, small, fenced, mitigation preserve adjacent to Fry's Electronics.

Quillworts, Spike-Moss & Pillworts: Primitive Pteridophytes, Some With Tree-Like Ancestors That Flourished During The Carboniferous Time 300 Million Years Ago    Isoetes (Quillwort)   Selaginella (Spike-Moss)   Pilularia (Pillwort)

Vernal Pool Field Near Palomar College   Pillworts & Quillworts Near Fry's Beautiful Rare Brodiaeas

Spike-moss (Selaginella) is an interesting pteridophyte that grows on boulders in the hills east of campus. Although often mistaken for a moss, this is a non-flowering, vascular plant that produces male and female sporangia in the leaf axils. There are 2 species on Owens Peak, S. bigelovii and S. cinerascens. Although horned lizards once roamed Owens Peak, I haven't seen one in years. They were often collected by people who tried to feed them lettuce and other greens. Their diet is 100 percent ants--mostly large black carpenter ants (Messor andrei) which are also rare on the peak (at least as of Jan. 2020).

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Ancient Cone-bearing Trees & Cycads

Any discussion of ancient plants would not be complete without mentioning cycads and cone-bearing trees with ancestors that lived during the dinosaur era. We have some excellent examples of this Jurassic flora on the Palomar College campus and Arboretum.

Cone-Bearing Trees & Cycads In Palomar Arboretum   Plants Of Jurassic Park: Living With Dinosaurs Distribution Of Cycads & Continental Drift Living Fossils At Palomar College

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All images on this page copyright © W.P. Armstrong