Rare Species Guide

  Basis for Listing

Cryptocolea imbricata (hidden-perianth liverwort) was originally described in 1951 (Schuster 1953) based on specimens from the Porcupine and Susie Islands in Cook County Minnesota (North Shore Highlands Subsection). Later, this apparently arctic species was found on the Chukotka Peninsula, Russia, in arctic Alaska, Greenland, and on Ellesmere Island (Schofield 2002). It has also been recorded from Isle Royale in the Upper Peninsula of Michigan. A search for the original Minnesota population has not yet been possible as the site is not easily accessible. However, no additional populations were found on nearby islands of the Susies’ Archipelago or on the mainland during surveys of suitable mesohabitat. The species’ biogeography is unique, and its habitat is susceptible to drying conditions and trampling. The long-term viability of C. imbricata depends on the maintenance of cool and moist habitat conditions. Given the species’ extreme rarity and limited geographic range in the state, its restrictive habitat requirements, the vulnerability of populations to degradation or destruction, and the concern over a range-wide decline because of climate change, C. imbricata was listed as a threatened species in 2013. 

  Description

Cryptocolea imbricata is a Jungermanniales (leafy liverwort), classified in either the Plagiochilaceae (Schuster 1953) or Jungermanniaceae (Schuster 1969). The plants are 5-9 mm (0.2-0.35 in.) long, quite fleshy, not or only slightly branched, bright green, with the older leaves becoming a yellowish-brown (Schuster 1953). The concave, spoon-like, and strongly imbricate leaves are not lobed, not even retuse, but entire and inserted so that the upper margin of each leaf is covered by the lower margin of the next leaf along. There are no under leaves, and the rhizoids are scattered or partly appearing in bundles. Leaf cells are thin-walled, with small trigones, (20)25(35) x (20)32(45) µm. Most characteristically, the perianth is completely hidden within bracts. Common species in Minnesota with similar facies are Mylia anomala, Chiloscyphus pallescens, Jungermannia leiantha, Jamesoniella autumnalis, and Plagiochila asplenioides. They are easily separated using diagnostic microscopic characters, but field characteristics are more subtle:  Mylia anomala frequently has pointed gemmae-bearing leaves and in the sun forms brown to fulvous patches; the other species might have some truncate-rectangular or even slightly retuse leaves or small under leaves; and Plagiochila asplenioides, when well-developed, has marginal teeth (when those are absent, the species is recognized by reflexed dorsal margins of the leaves, distinctly decurrent, also the leaf trace on the stem is uniquely non-linear, forming a stretched and extended S-shape).

  Habitat

Cryptocolea imbricata occurs on thin and moist soil overlying rocks and tolerates direct sunlight (Schuster 1969).  The plants occur scattered and widely dispersed and apparently never form pure mats or patches. In Greenland, the species is found in late-snowmelt areas or below persistent snow banks. In Minnesota, it was found on thin and moist soil on a rock ledge a few feet above the level of Lake Superior (Schuster 1953).

  Biology / Life History

No details of life history are known for C. imbricata. The apparent microhabitat in which it occurs, however, suggests it is a colonist or, more likely, a short-lived shuttle species (During 1979, 1992).

  Conservation / Management

Because C. imbricata is part of the “Tundra Strip” flora (Schuster 1957) and apparently requires a specific arctic-montane habitat, its populations may be susceptible to local extinction due to climate change

  Best Time to Search

The best time to search for C. imbricata is from May through September or essentially anytime the ground is not covered by snow.

  Conservation Efforts in Minnesota

The lone site for C. imbricata in Minnesota is on Susie Island in Lake Superior, which is now owned by the Grand Portage Band of Lake Superior Chippewa. Under band control, "human influence on the island will be kept to a minimum in order to protect areas of cultural significance as well as the natural environment".