| Buxbaumia | |
|---|---|
 | |
| Buxbaumia viridis | |
Scientific classification | |
| Kingdom: | Plantae |
| Division: | Bryophyta |
| Class: | Bryopsida |
| Subclass: | Buxbaumiidae Doweld |
| Order: | Buxbaumiales M.Fleisch. |
| Family: | Buxbaumiaceae Schimp. |
| Genus: | Buxbaumia Hedw., 1801[1] |
| Type species | |
| Buxbaumia aphylla Hedw. | |
| Species | |
Buxbaumia (bug moss,bug-on-a-stick,humpbacked elves, orelf-cap moss)[2] is a genus of twelve species ofmoss (Bryophyta). It was first named in 1742 byAlbrecht von Haller and later brought into modern botanical nomenclature in 1801 byJohann Hedwig[3] to commemorateJohann Christian Buxbaum, a German physician and botanist who discovered the moss in 1712 at the mouth of theVolga River.[2] The moss is microscopic for most of its existence, and plants are noticeable only after they begin to produce their reproductive structures. The asymmetrical spore capsule has a distinctive shape and structure, some features of which appear to be transitional from those in primitive mosses to most modern mosses.
Plants ofBuxbaumia have a much reducedgametophyte, bearing asporophyte that is enormous by comparison.[4] In most mosses, the gametophyte stage of thelife cycle is both green and leafy, and is substantially larger than the spore-producing stage. Unlike these other mosses, the gametophyte ofBuxbaumia is microscopic, colorless, stemless, and nearly leafless.[5][6] It consists exclusively of thread-likeprotonemata for most of its existence, resembling a thin green-black felt on the surface where it grows.[7] The plants aredioicous, with separate plants producing the male and female organs.[8] Male plants develop only one microscopic leaf around eachantheridium,[2][5] and female plants produce just three or four tiny colorless leaves around eacharchegonium.[3]
Because of its small size, the gametophyte stage is not generally noticed until the stalkedsporangium develops, and is locatable principally because the sporangium grows upon and above the tiny gametophyte.[6] The extremely reduced state ofBuxbaumia plants raises the question of how it makes or obtains sufficient nutrition for survival. In contrast to most mosses,Buxbaumia does not produce abundantchlorophyll and issaprophytic.[5] It is possible that some of its nutritional needs are met byfungi that grow within the plant.[3] However, a recent study of the chloroplast genome inBuxbaumia[9] failed to find any reduction in selective pressure on photosynthetic genes, suggesting that they are fully functional in photosynthesis, and that the moss is notmycoheterotrophic. This is also consistent with a lack of association between its rhizoids and nearby hyphae of soil fungi.[10]
The sporophyte at maturity is between 4 and 11 mm tall.[2] Thespore capsule is attached at the top of the stalk and is distinctive,[6] being asymmetric in shape and oblique in attachment.[11] As with most other Bryopsida, the opening through which the spores are released is surrounded by a doubleperistome (diplolepidious) formed from thecell walls of disintegrated cells.[12] The exostome (outer row) consists of 16 short articulated "teeth". Unlike most other mosses, the endostome (inner row) does not divide into teeth, but rather is a continuous pleated membrane around the capsule opening.[13] Only the genusDiphyscium has a similar peristome structure, although that genus has only 16 pleats in its endostome, in contrast to the 32 pleats inBuxbaumia.[3][12]Diphyscium shares withBuxbaumia one other oddity of the sporophyte; the foot (stalk base) ramifies as a result of outgrowths, so much so that they may be mistaken forrhizoids.[14]
Species ofBuxbaumia may be found across much of the temperate to subarctic regions of theNorthern Hemisphere, as well as cooler regions ofAustralia andNew Zealand.[6][8][15][16]
The moss is anannual orbiennial plant and grows indisturbed habitats or as apioneer species.[8][17] The plants grow on decaying wood, rock outcrops, or directly on the soil.[6][7] They do not grow regularly or reliably at given locations, and frequently disappear from places where they have previously been found.[7] Sporophyte stages begin their development in the autumn, and are green through the winter months.[7]Spores are mature and ready for dispersal by the late spring or early summer.[6][8] The spores are ejected from the capsule in puffs when raindrops fall upon the capsule's flattened top.[8]
The asymmetric sporophytes ofBuxbaumia aphylla develop so that the opening is oriented towards the strongest source of light, usually towards the south.[8] The species often grows together with the diminutiveliverwortCephaloziella, which forms a blackish crust that is easier to spot thanBuxbaumia itself.[8]
Buxbaumia is the only genus in the family Buxbaumiaceae, the order Buxbaumiales, and the subclass Buxbaumiidae.[18] It is thesister group to all other members of classBryopsida.[19][20] Some older classifications included theDiphysciaceae within the Buxbaumiales (or as part of the Buxbaumiaceae) because of similarities in theperistome structure,[3][12] or placed the Buxbaumiaceae in theTetraphidales.[21] However, recent phylogenetic studies based on genomic and transcriptomic data[22][23] clearly support it as the sister group of all otherBryopsida.
The genusBuxbaumia includes twelve species:
| genusBuxbaumia | |
| The species andphylogenetic position ofBuxbaumia.[18][20] | |
Because of the simplicity of its structure, Goebel interpretedBuxbaumia as a primitive moss, transitional between thealgae and mosses,[5] but subsequent research suggests that it is a secondarily reduced form.[8][20] The unusual peristome inBuxbaumia is now thought to be a transitional form between the nematodontous (cellular teeth) peristome of thePolytrichopsida and the arthrodontous (cell wall teeth) peristome of the Bryopsida.[20]
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