Another entry written by Taisha today:
Today's image of Adiantum pedatum was taken by swampr0se@Flickr on May 22, 2011. Ferns from this genus are among my favourites. I am drawn to the aesthetic contrast between the dark-coloured stipe and rachis to the bright green and glossy pinnules. Thanks swampr0se for the photo!
Adiantum pedatum of the Pteridaceae is one of about two hundred species in the genus Adiantum. Members of this genus are known for their glossy fronds that shed water readily and their gleaming blackish-brown stipes. Uniquely, this genus bears sporangia on the abaxial margins of the pinnules covered by a false indusium (formed by inrolling of the margins), rather than on the margin of the lamina like many other ferns. The arching fronds grow from creeping rhizomes that spread and form colonies over time. The fan-shaped blade is segmented into rounded lobes separated by shallow sinuses. This species sporulates from summer through autumn.
The northern maidenhair fern is found growing on humus-covered slopes and moist lime soils across eastern North America, however there are disjunct populations in China and other parts of eastern Asia. Adiantum pedatum is a part of the Adiantum pedatum complex comprising of three other species, Adiantum aleuticum, Adiantum myriosorum and Adiantum viridimontanum. Those species belonging to the Adiantum pedatum complex are characterised by pedately-divided frond clusters growing from clump-forming rhizomes. In a study looking at the biogeographic disjunction of the Adiantum pedatum complex between eastern Asia and North America by Lu et al., it was suggested that the Adiantum pedatum complex is of Asian origin dating to 4.27 million years ago (Ma) in the Pliocene. Migration to North America seems to have occurred in the late Pliocene to early Pleistocene via the Bering land bridge. Lu et al. also propose that the clades within North America, Adiantum pedatum and Adiantum aleuticum, dispersed back to eastern Asia about 0.8Ma, likely by way of the Aleutian Islands south of the Bering sea. (see: Lu J-M. et al. 2011. Biogeographic disjuction between eastern Asia and North America in the Adiantum pedatum complex (Pteridaceae). American Journal of Botany. 98(10):1680-1693.).