Pinnacles Nat. Mon. Trip #1
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Pinnacles & Sequoia-Kings Canyon Road Trip #1
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Part 1: Unusual & Colorful Lichens
© W.P. Armstrong 24 June 2012
Caliciaceae: Woven Spore Lichen (Texosporium sancti-jacobi)
A Rare & Endangered Crustose Soil Lichen That Grows On Rabbit Dung

During my botanical career I have taken many trips in search of little-known or unusual plants and lichens, but this species is certainly one of the most unusual. Texosporium sancti-jacobi is a rare lichen endemic to western North America. "Texo" is derived from the latin word "weave" and "sporium" refers to the fungal spores. The spores (ascospores) are tightly wrapped in an outer coating of interwoven fungal hyphae, an unusual trait only found in this species of lichen. In fact, this is the derivation of the peculiar common name of "woven spore lichen." It is known only from a few extremely small, localized and widely scattered populations in south-central Washington, central Oregon, southern Idaho, and central California. Some of the southern California populations have apparently been extirpated. It is typically restricted to soil microhabitats with small bits of decaying organic matter, such as decaying rabbit pellets, dead stems of Selaginella, stubble from dead tufts of bunchgrasses, small twigs in soil duff, and on other lichens. In California it is typically found growing on decaying rabbit pellets (also known as scat, dung & droppings). This latter habitat was the primary object of my road trip in June 2012.

Although this lichen was originally discovered around 1880 near San Diego, it was essentially forgotten or overlooked until the 1960s. It was recollected apparently near its type locality on Kearny Mesa; however, the area has been extensively developed. It has also been found on Clairemont Mesa but I have not verified these collection sites.

Left: Author and National Park Service Botanist Brent Johnson searching for Texosporium sancti-jacobi on rabbit droppings. Right: Examining a partically decomposed rabbit dropping (black arrow) with a hand lens. Sony T-9, an excellent macrophotography camera, in the foreground. Due to the rare and endangered status of this fragile lichen, the exact location in the central California Coast Range is not disclosed.

Typical habitat of Texosporium sancti-jacobi in the Central California Coast Range. The objects shaped like M&M'S® are old rabbit droppings (white arrow). After examining hundreds of rabbit droppings, I finally realized that the lichen was on smaller, partially decomposed droppings. None are visible in above image.

I carefully examined literally hundreds of rabbit droppings in search of Texosporium sancti-jacobi. The ground was so hot that it was uncomfortable to kneel. Obviously, June is not the best time to search for this lichen. One of the droppings in the above image is actually a puffed grain of the breakfast cereal Kix® desaturated (color removed) with Adobe Photoshop.

Finally, a rabbit dropping covered with the lichen Texosporium sancti-jacobi! The U.S. Penny is 19.0 mm in diameter.

Magnified view of a decomposed rabbit dropping covered by the whitish thallus of the unusual lichen Texosporium sancti-jacobi. Each cup-shaped apothecium (0.5 mm in diameter) contains a dark gray-olive green spore mass tinged with bright yellow, and an outer thalline rim. The rim may be gray like the thallus to yellowish-green depending on the soil moisture. The 2-celled ascospores are originally produced inside sac-like asci that soon burst and disintegrate, leaving a mass of spores and paraphyses called a mazaedium. [In a mazaedium, the hymenial layer lining the inside of the apothecium breaks down and all the asci release their spores.] Minute spores are wrapped in an outer coating of fungal hyphae, an unusual trait only found in this species of lichen. The greatest threat to the delicate soil crust and to this rare & unique species of lichen is loss of habit, including the following: Conversion of natural habitat to agricultural and suburban developments, invasion of annual weedy grasses, overgrazing, human recreational activities, and brush fires. Any of the above activities could completely annihilate a population of the lichen in a localized area.

  Another Member Of The Caliciaceae (Thelomma mammosum) That Forms A Mazaedium  

Above Image: Greatly magnified view of a decomposed rabbit dropping covered by the whitish thallus of the unusual lichen Texosporium sancti-jacobi. The cup-shaped apothecium in center is 0.5 mm in diameter. The rim may be dull gray to yellowish-green depending on the soil moisture. Minute spores are wrapped in an outer coating of fungal hyphae, an unusual trait unique to this species of lichen.

Left Image: To appreciate the size of one apothecium (0.5 mm), compare it with an average grain of ordinary table salt (NaCl) which is approximately 0.3 mm on a side.

Magnified view of the mature spores of Texosporium sancti-jacobi. Each spore is tightly wrapped with a layer of fungal hyphae (paraphyses). According to L. Tibell and A. van Hofsten (1968), the loose paraphyses become tightly appressed to the walls of the ascospores. Immature spores are 2-celled, but become darker and thicker with an outer fungal covering--thus obscuring the spore structure. Including their fungal coat, the spores range in size from 36-44 and 20-26 micrometers (0.036-0.044 and 0.020-0.026 mm). This is the only known lichen that produces spores with this unusual meshwork of fungal hyphae covering the spore wall, and is the derivation of the common name "woven spore lichen." According to B. McCune and R. Rosentreter (The Bryologist 95: 329-333, 1992), the unique fungal coat over the spores may increase their longevity. "The dark color of the coat may also increase survival in open habitats by providing some protection from ultraviolet radiation, and the chemical makeup of the spores may afford some antibiotic protection. These would be useful traits for a species that is tied to short-lived substrates (e.g. rabbit dung)." Magnification 500x and 700x.

  1. McCune, B., and R. Rosentreter. 1992. "Texosporium sancti-jacobi, a Rare Western North American Lichen." The Bryologist 95: 329-333.

  2. Tibell, T., and A. van Hofsten. 1968. "Spore Evolution of the Lichen Texosporium sancti-jacobi (= Cyphelium sancti-jacobi." Mycologia 60 (3): 553-558.

A single ascospore of Texosporium sancti-jacobi photographed at 1000x under oil immersion lens. The inverted color gives the fungal hyphae a bluish appearance. The meshwork of fungal hyphae surrounding the spore is clearly visible. This fungal coat is firmly attached to the spore wall and presumably provides protection and perhaps spore longevity. The actual spore beneath this dense fungal sheath is 2-celled.
The fungal spores (ascospores) of Texosporium sancti-jacobi are unique among lichens because they are tightly encased in a dense meshwork of fungal hyphae. The following image shows a variety of spores from other species of lichens that do not have this unusual fungal covering. Lichen spores come in many shapes and sizes, and are sometimes crucial to the correct identification of a species: They can be unicellular, 2-celled or partitioned into multiple sections like the squares of a Hershey's® chocolate bar. They can be clear and colorless or dark-colored (brown). The spores of Texosporium are actually 2-celled, but are obscurred by the dense fungal coat.

An assortment of spores from Wayne's Word lichen pages: A. Dimelaena radiata, B. Diploschistes sruposus, C. Verrucaria viridula, D. Diploschistes muscorum, E. Pyrenocollema halodytes (marine lichen), F. Rhizocarpon geminatum, G. Verrucaria maura (marine lichen), H. Thelomma mammosum. The latter species belongs to the same family Caliciaceae as Texosporium. Like Texosporium, the ascospores are originally produced inside sac-like asci that soon burst and disintegrate, leaving a mass of spores and paraphyses called a mazaedium.
  Lichen Images On Wayne's Word  

Flame Fire-Dot Lichen (Caloplaca ignea) in San Luis Obispo County

The following Caloplaca was adjacent to Caloplaca ignea on serpentine rock.