Microgramma / Solanopteris
Microgramma
Microgramma C.Presl is a genus of epiphytic ferns in the family Polypodiaceae, comprising approximately 30 speciesdistributed throughout the tropical and subtropical regions of Central and South America. Most species possess slender, creeping rhizomes and grow as epiphytes in tropical forests.
A distinct lineage within the genus consists of the four species formerly placed in the separate genus Solanopteris. These species develop strongly swollen rhizomes and are now included within Microgramma.
Myrmecophily has evolved several times within the genus. The former Solanopteris species possess tuberous rhizomes with internal cavities that serve as nesting sites for ants. In contrast, Microgramma megalophylla lacks swollen rhizomes but is nevertheless regularly inhabited by ants, which occupy the spaces between the rhizome and the substrate as shelter. In both cases, the ferns benefit from nutrients derived from organic material deposited by the ants.
The genus therefore illustrates that different forms of myrmecophily have evolved within an otherwise largely unspecialized group of ferns. The inclusion of the former genus Solanopteris within Microgramma is supported by both morphological characteristics and molecular phylogenetic studies.
Solanopteris bifrons
The rhizomes are thin and cord-like. Special short shoots branch off at regular intervals and grow into potato-like hollow outgrowths, which serve as nesting sites for the ants. Because of these "potatoes", Solanopteris species are also known as "potato ferns". The tubers have an opening on the underside. The structure is very reminiscent of the leaves of Dischidia major, which have been transformed into nesting structures.Native to South America, this ant fern can be found in the lowlands.The rhizome is covered with short, bristle-like outgrowths and is whitish-grey in colour. The fronds are divided, which gives the plants an extremely attractive appearance.The domatia of S. bifrons shimmer slightly metallic due to their micro-structures, are olive-green in colour and about the size of a walnut.The plants are supplied in different portion sizes.
Solanopteris bismarckii
The rhizomes are thin and cord-like. At regular intervals, special short shoots branch off and grow into potato-like hollow growths, which serve as nesting sites for ants. Because of these "potatoes", Solanopteris species are also known as "potato ferns". The tubers have an opening on the underside. The structure is very reminiscent of the leaves of Dischidia major, which have been converted into nesting structures. Solanopteris bismarckii occurs in Ecuador and Peru at medium altitudes. The shoots are greenish and scaly, and the leaves are undivided.The domatia of S. bismarckii have several conspicuous spiny outgrowths, giving them a morning star-like appearance.
Microgramma megalophylla
Microgramma megalophyllaMicrogramma megalophylla (Desv.) de la Sota is a widespread epiphytic fern in the family Polypodiaceae. The species occurs from Central America through the Caribbean to much of tropical South America, where it grows primarily in humid lowland rainforests. It is characterized by its long, creeping rhizomes and its conspicuously large, leathery, undivided fronds, which are considerably larger than those of most other species in the genus.Although M. megalophylla does not develop swollen rhizomes, it maintains a close association with ants. Its creeping rhizomes grow tightly appressed to the substrate, creating narrow spaces between the rhizome and the tree bark that are used by various ant species as nesting sites and passageways. The ants deposit organic material in these spaces, providing the fern with an additional source of nutrients. Unlike the former Solanopteris species, however, these nesting sites are not formed by specialized domatia or swollen rhizomes.A similar strategy is found in Lecanopteris mirabilis, several species of the genera Hoya and Dischidia, and the epiphytic cacti Deamia testudo and Strophocactus wittii. In all of these plants, ants occupy the natural spaces between the plant and the bark of the host tree without the formation of specialized domatia. Microgramma megalophylla therefore represents a remarkable example of a comparatively simple form of myrmecophily, in which a close symbiosis with ants has evolved without pronounced morphological specialization.