Smooth Cliffbrake

Pellaea glabella

With the Park still locked in winter we have been looking at evergreen species.  Last week we featured a rather rare, evergreen, limestone-loving fern, wall rue.  This week we take a look at another rather rare, evergreen limestone-loving fern of Wildwood Park, smooth cliffbrake.  This fern has compound leaves on a brown, or reddish grown, or purplish-brown stalk.  The leaflets can vary from almost round to long and narrow, and sometimes have ear-like lobes, as seen in the leftmost leaflet in the picture.  Sometimes, the leaflets are also divided into subleaflets.  Or, the lower part of the leaf may be divided while the upper part is simple.  Whatever the shape, the leaves are about 1 to 6 inches long and about one half to three inches wide.

Smooth cliffbrake likes limestone cliffs and ledges.  It ranges from  from southern Ontario to Quebec south to Pennsylvania and in the Appalachian Mountains to Virginia, west through Tennessee to Arkansas, Kansas, Iowa and Wisconsin.  It is also found in isolated populations ain Texas.  Like wall rue, it appears to be quite rare in Wildwood, being found, as far as I know, on only one boulder on the eastern slopes of the Park.  In fact it shares the boulder with wall rue, which can be seen in the lower part of the picture.  Should you find more plants than two, please let me know of them. 

Smooth cliffbrake can be confused with its relative, purple-stemmed cliffbrake (Pellaea atropurpurea).  In fact, smooth cliffbrake is known as Pellaea atropurpurea variety bushii in some books.  Purple-stemmed cliffbrake, however, is a larger species, with leaves up to 2 feet long, more reliably divided, and with a purplish-black stem.  It too likes limestone cliffs and ranges even more widely, from Quebec to Florida to Arizona.  It would not be at all surprising to find it in Wildwood, but no one has found it yet, to my knowledge. 

We learned earlier that ferns produce no flowers or fruits or seeds.  Instead they reproduce by producing spores.  The spores germinate to produce a tiny plant, rarely seen, which produces eggs and sperm.  When the sperm swims to the egg, a new fern begins to grow.  Smooth cliffbrake is an odd exception to this.  At one stage of spore formation, normal cell division fails, and the plant produces half as many spores with twice the normal number of chromosomes.  The spores germinate to form a tiny plant, but this plant fails to produce eggs, and instead, a normal fern grows up from its tissues.  Thus, each plant is a clone of the spore-producing mother plant.  These asexual forms are called variety glabella.   In the Ozark Mountains of Missouri there are a few isolated populations of smooth cliffbrake that reproduce by the normal sexual process; these plants are called Pellaea glabella missouriensis.  The asexual glabella variety has double the normal number of chromosomes as the variety missouriensis, and it is believed that at some time in the past, variety glabella arose from missouriensis by a doubling of the chromosomes and adoption of asexual reproduction.  It is interesting that the sexually aberrant form, ranging all over eastern Canada and the eastern United States is much more successful than the sexually normal form, restricted to a few spots in the Ozarks.

The ability of ferns to reproduce without producing flowers, seeds, or fruit, must have seemed amazing to people before the invention of microscopes enabled us to figure out what the spores were doing.  Hilderic Friend, in Flowers and Flower Lore (London, 1884) claims that the ability of ferns to multiply while keeping their reproduction quite invisible led many to suppose that ferns would be the key to developing invisibility potions.  Perhaps we now know what Harry Potter's cloak is made from?

The genus Pellaea, the cliffbrakes, occurs worldwide, but mostly in North and South America.  Ferns in this genus are typically adapted to dry habitats, like clffsides, and many members of the genus are found in the arid west.  The genus is part of the Pteridaceae, the Brake Family, or the Maidenhair Fern Family.

The common name cliffbrake is a compound of cliff, the common habitat for many of the species, and brake, which comes from the Middle English brake, meaning fern.  The name is related to bracken, which is another species of fern.  The genus name Pellaea comes from the Greek pellos, meaning "dark," and may refer to the dark bluish-green leaves of many of the species.  The species name, glabella, means smoothish, and refers to the stems, which, unlike those of other Pellaea species, have few or no hairs.

GGC