Selaginella, also known asspikemosses orlesser clubmosses, is a genus oflycophyte. It is usually treated as the only genus in the familySelaginellaceae, with over 750 known species.
This family is distinguished fromLycopodiaceae (the clubmosses) by having scale-leaves bearing a ligule and by havingspores of two types. They are sometimes included in an informal paraphyletic group called the "fern allies". The speciesS. moellendorffii is an importantmodel organism. Its genome has been sequenced by theUnited States Department of Energy'sJoint Genome Institute.[1] The nameSelaginella was erected by Palisot de Beauvois solely for the speciesSelaginella selaginoides, which turns out (with the closely relatedSelaginella deflexa) to be a clade that is sister to all otherSelaginellas, so any definitive subdivision of the species into separate genera leaves two taxa inSelaginella, with the hundreds of other species in new or resurrected genera.
Selaginella occurs mostly in the tropical regions of the world, with a handful of species to be found in the arctic-alpine zones of both hemispheres.[2] Fossils assignable to the modern genus are known spanning over 300 million years from the LateCarboniferous to the present.[3]
Selaginella species are creeping or ascendant plants with simple, scale-like leaves (microphylls) on branching stems from which roots also arise. The stems are aerial, horizontally creeping on the substratum (as inSelaginella kraussiana), sub-erect (Selaginella trachyphylla) or erect (as inSelaginella erythropus). The vascularsteles are polystelicprotosteles. Stem section shows the presence of more than two protosteles. Each stele is made up ofdiarch (having two strands of xylem[4]) andexarch (growing outward in)xylems.[citation needed] The steles are connected with the cortex by means of many tube-like structures calledtrabeculae, which are modified endodermal cells withcasparian strips on their lateral walls.[citation needed] The stems contain no pith.[citation needed]
InSelaginella, each microphyll and sporophyll has a small scale-like outgrowth called aligule at the base of the upper surface.[5]: 7 The plants areheterosporous with spores of two different size classes, known as megaspores and microspores.[6]
Unusual for the lycopods, which nearly always havemicrophylls with a single unbranched vein, the microphylls of a fewSelaginella species contain a branched vascular trace.[7]
Under dry conditions, some species ofSelaginella can survive dehydration. In this state, they may roll up into brown balls and be uprooted, but can rehydrate under moist conditions, become green again and resume growth. This phenomenon is known aspoikilohydry, and poikilohydric plants such asSelaginella bryopteris are sometimes referred to asresurrection plants.[8]
There is no evidence ofwhole genome duplication in Selaginella's evolutionary history. Instead they have gone through tandem gene duplications, which is particularly noticeable in genes relevant for desiccation tolerance.[9][jargon]
Their chloroplasts are missing about two-thirds of their plastidialtRNA genes, which are instead found in the genome of thenucleus.[10] The genus is unique among vascular plants in having species with monoplastidic cells, single giant chloroplasts, located mostly in their dorsal epidermal cells, but also in the upper mesophyll of some species. This appears to be a derived traits and an adaptation to low-light conditions, having originated at least twice. Cells with multiplastidic chloroplasts, more than ten chloroplasts per cell, are considered most basal, and are found in species exposed to more light. Oligoplastidic cells, cells with 3 to ten chloroplats, are more adated to weaker light, and the monoplastidic species being the most shade-loving forms. It is estimated that 70% of Selaginella species are monoplastidic. These receive just 0.4~2.1% of full sunlight, while species with multiple chloroplasts live in open places where they on average receive more than 40.5% of full sunlight.[11]
Some scientists still place the Selaginellales in the classLycopodiopsida (often misconstructed as "Lycopsida").[citation needed][12][13] Some modern authors recognize three generic divisions ofSelaginella:Selaginella,BryodesmaSojak 1992, andLycopodioidesBoehm 1760.Lycopodioides would include the North American speciesS. apoda andS. eclipes, whileBryodesma would includeS. rupestris (asBryodesma rupestre).Stachygynandrum is also sometimes used to include the bulk of species.[citation needed]
The first major attempt to define and subdivide the group was byPalisot de Beauvois[14] in 1803–1805. He established the genusSelaginella as a monotypic genus, and placed the bulk of species inStachygynandrum.Gymnogynum was another monotypic genus, but that name is superseded by his own earlier name ofDidiclis. This turns out, today, to be a group of around 45–50 species also known as theArticulatae, since his genusDidiclis/Gymnogynum was based onSelaginella plumosa. He also described the genusDiplostachyum to include a group of species similar toSelaginella apoda.Spring inflated the genusSelaginella to hold all selaginelloid species four decades later.
Phylogenetic studies by Korall & Kenrick[15][16] determined that theEuselaginella group, comprising solely the type species,Selaginella selaginoides and a closely related Hawaiian species,Selaginella deflexa, is a basal and anciently diverging sister to all otherSelaginella species. Beyond this, their study split the remainder of species into two broad groups, one including theBryodesma species, theArticulatae, sectionEricetorumJermy and others, and the other centered on the broadStachygynandrum group.
In 2023, Zhou & Zhang suggested that the genus should be broken up into 19 different genera.[17]
Selaginella canaliculataSelaginella selaginoidesSelaginella willdenowii is known for its iridescent colours
There are about 750 known species ofSelaginella.[21] They show a wide range of characters; the genus is overdue for a revision which might include subdivision into several genera.[citation needed] Species of spikemoss include:
A few species ofSelaginella aredesert plants known as "resurrection plants", because they curl up in a tight, brown or reddish ball during dry times, and uncurl and turn green in the presence of moisture. Other species are tropicalforest plants that appear at first glance to beferns.
A number ofSelaginella species are popular plants for cultivation, mostly tropical species. Some of the species popularly cultivated and actively available commercially include:
S. kraussiana: golden clubmoss
S. martensii: frosty fern
S. moellendorffii: gemmiferous spikemoss
S. erythropus: red selaginella or ruby-red spikemoss
^Clugston, M. (2014).Dictionary of Science (4th ed.). London: Penguin Reference Library. p. 743.ISBN978-0-141-98682-1.
^Walker, Peter (1992).Chambers Science and Technology Dictionary (4th ed.). Edinburgh NewYork: Chambers. p. 999.ISBN0-550-13239-2.
^Palisot de Beauvois (1805):Prodrome des cinquième et sixième familles de l'Æthéogamie, les mousses, les lycopodes.
^Korall, P. & Kenrick, P. (2002), "Phylogenetic relationships in Selaginellaceae based onrbcL sequences",American Journal of Botany,89 (3):506–17,doi:10.3732/ajb.89.3.506,PMID21665649
^Korall & Kenrick (2004): The phylogenetic history of Selaginellaceae based on DNA sequences from the plastid and nucleus: extreme substitution rates and rate heterogeneity.Molecular Phylogenetics and Evolution, Volume 31, Issue 3, June 2004, Pages 852–864
^abZhou, Xin-Mao; Zhang, Li-Bing (2015), "A classification ofSelaginella (Selaginellaceae) based on molecular (chloroplast and nuclear), macromorphological, and spore features",Taxon,64 (6):1117–1140,doi:10.12705/646.2,S2CID90451945
Media related toSelaginella at Wikimedia Commons
Data related toSelaginella at Wikispecies
