Soil Ecology and Restoration Group
Mesa club moss (Selaginella cinerascens) is not really a moss but is more closely related to the ferns and is known as a fern ally (Stotler, 1996; Lellinger, 1985). These poikilohydric plants are able to tolerate very deep desiccation with rapid recovery when moisture levels increase. They green up and return to life within minutes of watering and can dry down and appear lifeless by the next morning.
Mesa club moss is an important component of the soil surface ecosystem in many parts of coastal San Diego, while Selaginella bigelovii is found further inland (Beauchamp, 1986). These plants are prostrate and often provide nearly complete coverage of the soil in an ashy gray green carpet (Munz and Keck, 1973). Mesa club moss forms a tough mat with extensive roots that is very resistant to erosion. A garden hose with a nozzle can be sprayed directly onto a well developed Mesa club moss mat without causing any erosion. The Mesa club moss mats are usually found in less disturbed areas in association with native grasses, flowers, and shrubs. Mesa club moss is vulnerable to trampling and during the severe overgrazing of the mid 1800s the Selaginalla cover was probably greatly reduced, but it has recovered in some areas. Limited sampling of Selaginella soils showed considerably higher levels of micronutrients such as zinc (mean 7.1 ppm) and copper (mean 1.3 ppm), lower nitrate levels (mean 6 ppm), and more organic matter (mean 3.7%), than adjacent disturbed and very disturbed soils.
The reproductive cycle of ferns consists of two generations, asexual (sporophyte) and sexual (gametophyte). Gametophytes produce gametes (eggs and sperm) that fuse, giving rise to the sporophyte generation. Sporophytes produce asexual spores which germinate to produce a small, sexual plant (gametophyte) called the prothallium. In Selaginella, male and female prothalli are formed and confined within the spore walls. The spores are formed in sporangia which are 1-celled, sub-globose, and solitary. The sporangia develop near the base of ordinary leaves, or on modified leaves (sporophylls) that form more or less 4-angled cones (strobili) at the tips of the branches. The spores are clustered in small cones or borne in the axils of the scale-like leaves.
Little is known about sexual distribution in Selaginella. Light microscopy of Selaginella species showed that proximal most branches had fewer female sporangia while distal branches had more, and terminal branches had more male strobili (Hill, 1996). Selaginella is heterosporous, forming two types of spores: one to four megaspores, usually in the lower part of the cone; and numerous minute, reddish to orange, microspores, usually in the upper part of the cone. The male prothallus develops within the microspore and forms male sex cells; the female prothallus develops from the megaspore and forms female sex cells (Munz and Keck, 1973). Only one sporophyte plant develops from each prothallium, and after development has begun, the parent prothallium dies. Reproduction of natural populations is not well studied or understood.
Growth of the Mesa club moss appears to be slow under natural conditions, typically measured in mm per year, but cut slopes more than two feet wide from the late 1960s have been covered in some locations at USIU. From observations and experiments in appears likely to grow only in winter when it is damp for several days in a row and when humidity is high, these conditions are rare, and during the winter of 1999-2000 were exceedingly rare. Irrigating when the air is dry has not been effective in accelerating growth, perhaps because of salinity or chlorine in the water or the rapid drydown of the surface if a major storm system is not moving through the area.
Propagation experiment 1999-2000
Relatives of Mesa club moss are propagated for sale as groundcover or house plants, but little is known about the local club mosses. They have proved difficult to propagate effectively in several years of experiments. Bowler (1999) reported fairly good results in transplanting plugs, so in June 1999 we started an experiment on a degraded site at USIU (in an area where natural populations are found) to examine establishment of plugs and fragments in the field following recommended greenhouse procedures from similar species.
Forty eight plugs were cut from adjacent Selaginella fields with a piece of stainless steel pipe with teeth cut in the end. The forty eight sets of fragments were broken out of moss dug with a shovel, amounts were matched by eye. This was a full factorial experiment in two blocks contrasting the effects of covering these two alternative propagules with glass, plastic, with a control of no covers; and limited fertilizer or no fertilizer.
Figure 5-1. Block of Selaginella treatments
The glass covers were single strength glass, the plastic covers were twin wall polycarbonate, and the fertilizer was 1/2 ounce per gallon of Miracle Grow, applied with a squirt bottle at 200 ml per treatment over three treatments. Plants were watered once every two to three days for several weeks after transplanting, then once every two weeks, then once a month and with no additional watering after late fall. The glass and plastic covers were vandalized twice in the winter of 1999-2000 and were not fully replaced after the second attack so changes seen in survival represent effects primarily from 1999.
Figure 5-2. Glass covered Selaginella plug
Overall survival was good from plugs, 69% and tolerable from fragments 62%, but growth was very limited. The plugs were in much better condition, with a mean health rating of 1.9 (out of four) for the plugs and 0.9 for the fragments. The combined effects of propagation method and cover are shown in figure 5-3.
The effects of the propagation methods were statistically different, with a p value of 0.0001. The covers were detrimental, reducing the health of the fragments and plugs, contrary to propagation suggestions. The mean health rating of uncovered propagules was 2, for glass 1.3 and plastic 0.9. This was statistically significant with a p value of 0.0015. Survival was 90% for both fertilized and unfertilized uncovered plugs. Survival of fragments was 80% for both fertilized and unfertilized uncovered plugs. The limited fertilizer addition appeared to provide some benefit by increasing the health rating from 1.35 to 1.46, but was not statistically significant. There were no statistically significant differences between blocks.
Health rating: 4 = excellent, 3 = good, 2 = fair, 1 = poor, 0 = dead
Figure 5-3. Selaginella health rating by propagation method and cover after one year
It appears likely that the best strategy is to use plugs transplanted to containers or directly to the field without covers and with fertilizer. The covers may have baked the propagules and killed them (Bainbridge, 1990). Additional fertilizer may have been produced better results. The use of tap water for irrigation (chlorine and salt) may also have inhibited growth and reduced survival.
Accelerating growth with careful management of moisture, amendments and nutrients is essential for commercial use of Mesa club moss. We will continue experiments in 2000-2001 comparing the benefits of distilled water and additional fertilizer on bare plugs.
An additional treatment yet to be attempted is the collection and sowing of mega and microspores. This method is reported to be slow, yet very effective. This may be due to difference in collection (easier to collect live, green fragments during growth) or other factors such as air temperature, humidity or presence of spores.
The spike mosses appear to have excellent potential for soil stabilization and may eventually become a useful component of restoration projects if propagation can be made economical and effective. So far it has been possible to speed growth and spread. Ultimately it may be possible to develop a Selaginella mat that could be unrolled on an erosive slope like laying sod. These may also be effective for median strips where conditions are extremely harsh.