Asplenium ruta-muraria & Asplenium trichomanes

Asplenium ruta-muraria

Perennial of the Aspleniaceae family, this small fern is one of the most common and cosmopolitan of the genus: it is present throughout almost all of Europe, temperate Asia, North Africa, and North America. It is confined to limestone rock crevices, old stone walls, ruins, and ancient masonry, from sea level up to over 2,000 meters in mountainous regions.

It forms very dense, persistent small tufts, only 3 to 15 cm in height, with fronds that are triangular to oval in their general outline, bipinnate to tripinnate, with short pinnules, wedge-shaped to subrhomboidal, of a matte dark green, slightly leathery. The cut and geometric outline of the fronds vaguely evokes the leaves of the garden rue, Ruta graveolens, which is the origin of its epithet.

The sori are oblong, arranged in convergent lines on the underside of the pinnules, covered with a whitish indusium that browns with maturity. In its natural habitat, spore production extends from June to September. It is a remarkably cold and drought-resistant fern, capable of colonizing crevices barely a few millimeters wide in walls exposed to full sun.

In cultivation, it requires a very poor limestone substrate and perfect drainage; it readily naturalizes in the joints of old walls and dry limestone rock gardens, without requiring any particular maintenance once established.

 

Asplenium trichomanes

Perennial of the Aspleniaceae family, this fern with a circumboreal distribution is one of the most widespread of the genus: it is found on all continents, from temperate zones to subalpine regions, generally between sea level and 2,500 meters in altitude. It colonizes rock crevices, shaded rocky walls, old walls, and screes, on both limestone and siliceous substrates depending on the subspecies.

It forms small, spreading, persistent rosettes, 5 to 20 cm in height, immediately recognizable by their linear and pinnate fronds, bearing numerous oval to suborbicular pinnules, of a bright to medium green, regularly arranged on either side of a shiny, persistent dark brown-black rachis. This dark and shiny rachis, visible in the photograph where it contrasts sharply with the tender green of the pinnules, constitutes the most distinctive and elegant feature of the species.

The sori are oblong, arranged in rows on the underside of the pinnules. In its natural habitat, spore production extends from May to October. Several subspecies are recognized, differing notably in their calcicolous or silicicolous affinity.

In cultivation, it requires a well-drained substrate, exposure to shade or partial shade, and a certain ambient humidity. It easily naturalizes in wall crevices and shaded rock gardens, and withstands harsh winters without special protection.