Rare Species Guide

  Synonyms

Lycopodium porophilum, Huperzia selago var. porophila, Lycopodium selago var. patens

  Basis for Listing

This lycophyte has a number of scattered population centers in the north central and east central parts of the country, but it is considered rare in most of the states where it occurs. Habitats are consistently associated with moist, sheltered cliffs, usually on sandstone bedrock. However, Huperzia porophila (rock fir moss) seems to be rare even where suitable habitat exists. This is certainly the case in Minnesota. Historic populations documented by herbarium specimens collected in Blue Earth County in 1883 and in Hennepin County in 1902, have not been relocated and may no longer be extant. There are only a very few populations known to currently exist in isolated habitats in the southeast (The Blufflands Subsection) and northeast (Northern Superior Uplands Section) corners of the state. Given its rarity, H. porophila was listed as a threatened species in Minnesota in 1984.

  Description

The genus Huperzia in Minnesota consists of 4 species: H. porophila, H. lucidula (shining fir moss), H. appressa (Appalachian fir moss), and H. selago (northern fir moss), and a wide assortment of their hybrids. Since H. porophila is believed to be an allopolyploid that began its existence long ago as a chance fertile hybrid between H. appressa and H. lucidula, it has characteristics of both species. Visually, it seems to most closely resemble H. lucidula, but it occurs on cliffs like H. appressa rather than in forests like H. lucidula.

For practical purposes, H. porophila can be distinguished from the other 3 species by its short slender rooting bases (as compared to the sprawling elongate bases of H. lucidula); flat leaf bases (as compared to the plump hollow leaf bases of H. selago); stomata numbering less than 50 on the upper surface of a typical leaf (as compared to more than 60 per leaf for similar species). To be certain that a particular plant is not a hybrid usually requires a microscopic examination of the spores to see if a high percentage are abortive (any percentage greater than 40 percent indicates a hybrid). It may be necessary to consult a specialist at some point.

  Habitat

Prior to 2000, all Minnesota records of H. porophila had been had been found on ledges on sandstone cliffs and outcrops in the southeastern part of the state. Intensive field searches that began in 2000, found the species at a small number of sites in northeastern Minnesota on diabase cliffs, which are somewhat different in nature than sandstone. Whether on sandstone or diabase, sites are typically north-facing, wooded habitats that are moist and well shaded. Throughout its Minnesota range, H. porophila occurs with other Huperzia species and hybrids, especially H. lucidula, H. appressa, H. ×bartleyi (Bartley's fir moss), and H. ×buttersii (Butters' fir moss). Typically, H. porophila is much less abundant than other Huperzia spp. at a given site.

  Biology / Life History

Vegetative growth begins in the spring or early summer and continues for most of the growing season. The plant is evergreen and perennial and continues to grow 2-4 cm (0.8-1.6 in.) a year for 4 or 5 years. At that time, the plant will have reached reproductive maturity. It will continue to grow for perhaps another 4 or 5 years, producing spores and gemmae each year. At the end of this time, it will senesce and die. It is considered to have a determinate life cycle, because its life span is determined by its biology rather than environmental conditions. Sporangia are produced during the first part of the growing season, dehiscing in autumn of the following year. Gemmae are produced in late summer and are dispersed about one year later. The spores function in sexual reproduction; the gemmae are a type of vegetative reproduction. Production and dispersal of gemmae are thought to be the primary mechanism for maintaining the population. Hybrids are common and are often found in mixed populations with H. lucidula, H. selago, H. appressa, and H. porophila.

  Conservation / Management

Habitat for H. porophila is limited in Minnesota. Potentially suitable habitats can be found only in the Lower Mississippi and Minnesota River valleys and in scattered sites in the Arrowhead region. But even where suitable habitat is available, H. porophila rarely occurs. However, because of the resemblance of this species to more common Huperzia species and hybrids, and its propensity to grow in mixed colonies, some populations may have been inadvertently overlooked. Targeted searches in regions of the southeast where sandstone bedrock occurs at the surface and diabase cliffs in the northeast may uncover new populations.

Even though the cliff habitats of this species might seem durable and not easily damaged, the rare plant assemblages that occur on them are extremely fragile. They are shallowly rooted in crevices and typically occur in low numbers. Huperzia porophila occurrences warrant protection from recreational uses such as rock-climbing and scrambling (non-technical rock hopping and exploration).

  Best Time to Search

Plants are visible throughout the growing season, but because spores may be needed for positive identification, searches for Huperzia porophila should be conducted from mid-summer through fall.

  Conservation Efforts in Minnesota

Known populations of H. porophila currently exist on State Forest lands, State Park lands, National Forest land, and on the property of a private environmental learning center. These sites are presumably well protected from most development activities that might threaten this species, such as rock quarrying, but the subtler threats posed by recreational use of cliff habitats have not been fully addressed.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.

Peck, J. H. 1982. Ferns and fern allies of the driftless area of Illinois, Iowa, Minnesota, and Wisconsin. Milwaukee Public Museum Press Contributions in Biology and Geology No. 53, Milwaukee, Wisconsin. 140 pp.

Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.

Wagner, W. H., Jr., and J. M. Beitel. 1993. Huperzia. Pages 20-24 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York, New York.