Buxbaumia
Encyclopedia
Buxbaumia is the botanical name
for a genus of twelve species of moss
(Bryophyta). It was named in 1801 by Johann Hedwig
to commemorate Johann Christian Buxbaum
, a German physician and botanist who discovered the moss in 1712 at the mouth of the Volga River
. 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.
, bearing a sporophyte
that is enormous by comparison. In most mosses, the gametophyte stage of the life cycle
is both green and leafy, and is substantially larger than the spore-producing stage. Unlike these other mosses, the gametophyte of Buxbaumia is microscopic, colorless, stemless, and nearly leafless. It consists exclusively of thread-like protonema
ta for most of its existence, resembling a thin green-black felt on the surface where it grows. The plants are dioicous
, with separate plants producing the male and female organs. Male plants develop only one microscopic leaf around each antheridium
, and female plants produce just three or four tiny colorless leaves around each archegonium
.
Because of its small size, the gametophyte stage is not generally noticed until the stalked sporangium
develops, and is locatable principally because the sporangium grows upon and above the tiny gametophyte. The extremely reduced state of Buxbaumia plants raises the question of how it makes or obtains sufficient nutrition for survival. In contrast to most mosses, Buxbaumia does not produce abundant chlorophyll
and is saprophytic. It is possible that some of its nutritional needs are met by fungi that grow within the plant.
The sporophyte at maturity is between 4 and 11 mm tall. The spore
capsule is attached at the top of the stalk and is distinctive, being asymmetric in shape and oblique in attachment. As with most other Bryopsida, the opening through which the spores are released is surrounded by a double peristome
(diplolepidious) formed from the cell wall
s of disintegrated cells. 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. Only the genus Diphyscium has a similar peristome structure, although that genus has only 16 pleats in its endostome, in contrast to the 32 pleats in Buxbaumia. Diphyscium shares with Buxbaumia one other oddity of the sporophyte; the foot (stalk base) ramifies as a result of outgrowths, so much so that they may be mistaken for rhizoid
s.
, as well as cooler regions of Australia
and New Zealand
.
The moss is an annual
or biennial plant
and grows in disturbed habitats or as a pioneer species
. The plants grow on decaying wood, rock outcrops, or directly on the soil. They do not grow regularly or reliably at given locations, and frequently disappear from places where they have previously been found. Sporophyte stages begin their development in the autumn, and are green through the winter months. Spore
s are mature and ready for dispersal by the late spring or early summer. The spores are ejected from the capsule in puffs when raindrops fall upon the capsule's flattened top.
The asymmetric sporophytes of Buxbaumia aphylla develop so that the opening is oriented towards the strongest source of light, usually towards the south. The species often grows together with the diminutive liverwort
Cephaloziella, which forms a blackish crust that is easier to spot than Buxbaumia itself.
. Some older classifications included the Diphysciaceae
within the Buxbaumiales (or as part of the Buxbaumiaceae) because of similarities in the peristome
structure, or placed the Buxbaumiaceae in the Tetraphidales. Most recent cladistic
studies using DNA sequences are not conclusive regarding the relationship between Buxbaumia and Diphyscium, but evidence suggests they are separate lines of a paraphyletic group. No recent studies favor a placement with the Tetraphidales.
The genus Buxbaumia includes twelve species:
Because of the simplicity of its structure, Goebel interpreted Buxbaumia as a primitive moss, transitional between the algae
and mosses, but subsequent research suggests that it is a secondarily reduced form. The unusual peristome in Buxbaumia is now thought to be a transitional form between the nematodontous (cellular teeth) peristome of the Polytrichopsida and the arthrodontous (cell wall teeth) peristome of the Bryopsida.
Botanical name
A botanical name is a formal scientific name conforming to the International Code of Botanical Nomenclature and, if it concerns a plant cultigen, the additional cultivar and/or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants...
for a genus of twelve species of moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
(Bryophyta). It was named in 1801 by Johann Hedwig
Johann Hedwig
Johann Hedwig , also seen as Johannes Hedwig or Latinised as Joannis Hedwig, was a German botanist notable for his studies of mosses , in particular the observation of sexual reproduction in the cryptogams.He was born in Romania, and studied medicine at the University of Leipzig,...
to commemorate Johann Christian Buxbaum
Johann Christian Buxbaum
Johann Christian Buxbaum , was a German physician, botanist and traveller.He was born in Merseburg and studied medicine at the Universities of Leipzig, Wittenberg, Jena, and Leyden....
, a German physician and botanist who discovered the moss in 1712 at the mouth of the Volga River
Volga River
The Volga is the largest river in Europe in terms of length, discharge, and watershed. It flows through central Russia, and is widely viewed as the national river of Russia. Out of the twenty largest cities of Russia, eleven, including the capital Moscow, are situated in the Volga's drainage...
. 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.
Description
Plants of Buxbaumia have a much reduced gametophyteGametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
, bearing a sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
that is enormous by comparison. In most mosses, the gametophyte stage of the life cycle
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
is both green and leafy, and is substantially larger than the spore-producing stage. Unlike these other mosses, the gametophyte of Buxbaumia is microscopic, colorless, stemless, and nearly leafless. It consists exclusively of thread-like protonema
Protonema
A protonema is a thread-like chain of cells that forms the earliest stage of a bryophyte life cycle...
ta for most of its existence, resembling a thin green-black felt on the surface where it grows. The plants are dioicous
Monoicous
Monoicous is a botanical term used to describe plants which bear both sperm and eggs on the same gametophyte. Dioicous is the complementary term describing species in which gametophytes produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of...
, with separate plants producing the male and female organs. Male plants develop only one microscopic leaf around each antheridium
Antheridium
An antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
, and female plants produce just three or four tiny colorless leaves around each archegonium
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
.
Because of its small size, the gametophyte stage is not generally noticed until the stalked sporangium
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
develops, and is locatable principally because the sporangium grows upon and above the tiny gametophyte. The extremely reduced state of Buxbaumia plants raises the question of how it makes or obtains sufficient nutrition for survival. In contrast to most mosses, Buxbaumia does not produce abundant chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
and is saprophytic. It is possible that some of its nutritional needs are met by fungi that grow within the plant.
The sporophyte at maturity is between 4 and 11 mm tall. The spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
capsule is attached at the top of the stalk and is distinctive, being asymmetric in shape and oblique in attachment. As with most other Bryopsida, the opening through which the spores are released is surrounded by a double peristome
Peristome
The word peristome is derived from the Greek peri, meaning 'around' or 'about', and stoma, 'mouth'. It is a term used to describe various anatomical features that surround an opening to an organ or structure. The term is used in plants and invertebrate animals, such as in describing the shells of...
(diplolepidious) formed from the cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s of disintegrated cells. 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. Only the genus Diphyscium has a similar peristome structure, although that genus has only 16 pleats in its endostome, in contrast to the 32 pleats in Buxbaumia. Diphyscium shares with Buxbaumia one other oddity of the sporophyte; the foot (stalk base) ramifies as a result of outgrowths, so much so that they may be mistaken for rhizoid
Rhizoid
Rhizoids are thread-like growths from the base or bottom of a plant, found mainly in lower groups such as algae, fungi, bryophytes and pteridophytes, that function like roots of higher plants ....
s.
Distribution and ecology
Species of Buxbaumia may be found across much of the temperate to subarctic regions of the Northern HemisphereNorthern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
, as well as cooler regions of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
.
The moss is an annual
Annual plant
An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...
or biennial plant
Biennial plant
A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots , then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming...
and grows in disturbed habitats or as a pioneer species
Pioneer species
Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...
. The plants grow on decaying wood, rock outcrops, or directly on the soil. They do not grow regularly or reliably at given locations, and frequently disappear from places where they have previously been found. Sporophyte stages begin their development in the autumn, and are green through the winter months. Spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s are mature and ready for dispersal by the late spring or early summer. The spores are ejected from the capsule in puffs when raindrops fall upon the capsule's flattened top.
The asymmetric sporophytes of Buxbaumia aphylla develop so that the opening is oriented towards the strongest source of light, usually towards the south. The species often grows together with the diminutive liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
Cephaloziella, which forms a blackish crust that is easier to spot than Buxbaumia itself.
Classification
Buxbaumia is the only genus in the family Buxbaumiaceae, the order Buxbaumiales, and the subclass Buxbaumiidae. It is the sister group to all other members of class BryopsidaBryopsida
The Bryopsida constitute the largest class of mosses, containing 95% of all moss species. It consists of approximately 11,500 species, common throughout the whole world....
. Some older classifications included the Diphysciaceae
Diphysciaceae
Diphyscium is a genus of mosses in the family Diphysciaceae. Members of this genus are small, perennial plants. The capsule does not elongate much, and remains buried among surrounding leaves.There are fifteen species of Diphyscium...
within the Buxbaumiales (or as part of the Buxbaumiaceae) because of similarities in the peristome
Peristome
The word peristome is derived from the Greek peri, meaning 'around' or 'about', and stoma, 'mouth'. It is a term used to describe various anatomical features that surround an opening to an organ or structure. The term is used in plants and invertebrate animals, such as in describing the shells of...
structure, or placed the Buxbaumiaceae in the Tetraphidales. Most recent cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
studies using DNA sequences are not conclusive regarding the relationship between Buxbaumia and Diphyscium, but evidence suggests they are separate lines of a paraphyletic group. No recent studies favor a placement with the Tetraphidales.
The genus Buxbaumia includes twelve species:
genus Buxbaumia
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| The species and phylogenetic Phylogenetics In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices... position of Buxbaumia. |
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Because of the simplicity of its structure, Goebel interpreted Buxbaumia as a primitive moss, transitional between the algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and mosses, but subsequent research suggests that it is a secondarily reduced form. The unusual peristome in Buxbaumia is now thought to be a transitional form between the nematodontous (cellular teeth) peristome of the Polytrichopsida and the arthrodontous (cell wall teeth) peristome of the Bryopsida.
External links
- W. B. Schofield. 2004. Bryophyte Flora of North America: Buxbaumiaceae