November EcoQuest – Spotting Spike-moss

Not all members of the flora of Colorado produce flowers and seeds. Some, such as ferns, reproduce by spores. Spike-mosses, or Selaginella, are ferns and the sole genus in the family Selaginellaceae. Unlike some other ferns, spike-mosses have two different types of spores (megaspores and microspores) that occur in megasporangia and microsporangia located at the base of leafy branches called sporophylls. The sporophylls are only slightly differentiated from the vegetative leaves in 4-sided structures. The sporangia type can be differentiated by the color – megasporangia containing megaspores are greenish while microsporangia containing microspores are orangish.

Selaginella species are creeping plants with scale-like leaves, and can be found growing on rocky cliffs, ledges, in rocky crevices, and on rock outcroppings. The leaves of spike-mosses remain green year-round, making them a good plant to hunt for when plants have stopped blooming. There are four species of Selaginella occurring in the Denver-Boulder metro area: Selaginella densa, S. mutica, S. underwoodii, and S. weatherbiana.

Selaginella densa is easily distinguished by its densely matted growth form with short, compact branches, while the other two species are loosely matted with long, spreading branches. Selaginella densa is also our most observed spike-moss in the metro area. The other three species are more subtly distinguished among. Selaginella weatherbiana can be determined by the growth habit – at branch forks, S. weatherbiana has larger branches that continue to grow as a vegetative shoot and a shorter, smaller one that forms a fertile branch. Lastly, S. mutica leaves lack a bristle tip while S. underwoodii leaves have a short bristle tip present. This bristle tip is best viewed under a microscope or with a hand lens.

See if you can locate some Selaginella and help Denver Botanic Gardens by photographing as many plants as possible in the month of November. Post your findings to iNaturalist so they will automatically be added to the Denver EcoFlora Project.

Posted on October 31, 2022 06:59 PM by jackerfield