Ptilidium
Encyclopedia
Ptilidium is a genus of liverwort
, and is the only genus
in family
Ptilidiaceae. It includes only three species: Ptilidium californicum
, Ptilidium ciliare, and Ptilidium pulcherrimum. The genus is distributed throughout the arctic and subarctic, with disjunct populations in New Zealand and Tierra del Fuego. Molecular analysis suggests that the genus has few close relatives and diverged from other leafy liverworts early in their evolution.
, the underleaves are not significantly smaller than the lateral leaves. The "flossy" appearance from the leaf edges, together with the characteristic yellowish-brown or reddish-brown color make the genus easy to recognize.
Like Ptilidium, Blepharostoma and Trichocolea have deeply divided leaves with marginal cilia, however Ptilidium differs from these other two genera in that its leaf cells have bulging trigone
s (thickenings at the corners between cell wall
s).
The plants grow in dense mats, with stems growing either prostrate or ascending. Individual stems are once or twice pinnate
, rarely with branches and only a few short rhizoid
s. The leaves are incubous
and divided deeply into three to five portions, and edges of the leaf divisions are fringed with cilia. The underleaves are similar to the lateral leaves, but are slightly smaller. All species are dioicous, producing antheridia
and archegonia
on separate plants. The archegonia are terminal on a main stem. Mature sporophyte
s develop from within a large perianth with three distal folds.
The three species in the genus may be distinguished by the density of cilia along the leaf margin, depth of lobing in the leaf, width of the leaf base, and the substrate on which it is found growing. P. californicum has few cilia along the edge of its leaves and has underleaves lobed to about seven-eighths of their length. The other two species have many marginal cilia and underleaves lobed to no more than half their length. P. ciliare usually grows on soil and has leaf lobes that are 15–20 cells wide at their base. P. pulcherrimum usually grows on wood or rock, and has leaf lobes normally 6–10 cells wide at their base.
distribution, and is found in abundance in coniferous forests of Europe
, Asia
, and North America
, as well as in New Zealand
and Tierra del Fuego
. Plants often grow attached to the bark of trees in the northern hemisphere, but may occur in rocks in mountain districts of New Zealand. At the more temperate ends of its range, plants are restricted to higher elevations.
Schuster (1984) proposed that the disjunct distribution of Ptilidium ciliare between the northern and southern hemispheres could be explained by migration of the Indian Plate from Gondwana
. In this hypothesis, P. ciliare is a species originally native to Gondwana, and sterile populations existing in modern New Zealand and Tierra del Fuego are relict
s of this earlier distribution. The other two species of Ptilidium are thus believed to be later descendants. Schuster's hypothesis is partially based upon a belief that Ptilidium is related to the genera Mastigophora and Dendromastigophora, both of which are largely restricted to the southern hemisphere. However, this relationship is not supported by modern molecular analysis, which places Mastigophora in an entirely different part of the liverwort phylogeny. Instead, Ptilidium is now believed to be part of an isolated clade allied only to two East Asian endemics, and it is thus more likely that the sterile populations of Ptilidium in the southern hemisphere reflect long-distance dispersal of plant fragments. Ptilidium ciliare is tolerant of desiccation and is ubiquitous in the Arctic, but rarely produces spore
s, and it is therefore believed to spread by means of such fragments.
The diagram at left summarizes a portion of a 2006 cladistic analysis
of liverworts based upon three chloroplast genes, one nuclear gene, and one mitochondrial gene. The genus Trichocoleopsis was not included in the original broad analysis, but is the sister taxon of Neotrichocolea according to a more narrowly focussed study utilizing six chloroplast genes, two nuclear genes, and a mitochondrial gene.
The genus Ptilidium is sister to the Trichocoleopsis-Neotrichocolea clade. This combined clade, in turn, attaches at the base of a large clade (2600 species) designated "Leafy II". That clade, together with "Leafy I" (another 1800 species) and Pleurozia
constitute the Jungermanniales
, as traditionally defined. Ptilidium, Neotrichocolea, and Trichocoleopsis thus sit at the base of the Jungermanniales, at a point where the two major groups of leafy liverworts diverge from each other.
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....
, and is the only genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
in family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Ptilidiaceae. It includes only three species: Ptilidium californicum
Ptilidium californicum
Ptilidium californicum is a rare liverwort of the Western U.S.- Technical description :Plants dioicous, small but medium-sized for a liverwort, from golden-green to golden, but more typically reddish-brown, or dilute purplish-red, or coppery red, resembling a dense fuzzy mat, occurring in small or...
, Ptilidium ciliare, and Ptilidium pulcherrimum. The genus is distributed throughout the arctic and subarctic, with disjunct populations in New Zealand and Tierra del Fuego. Molecular analysis suggests that the genus has few close relatives and diverged from other leafy liverworts early in their evolution.
Description
The name of the genus comes from the Greek word ptilidion for "small feather", in reference to the multiply deeply-divided leaves with fringed edges, which give the plant a "feathery" appearance. Unlike other leafy liverwortsJungermanniales
Jungermanniales is the largest order of liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem...
, the underleaves are not significantly smaller than the lateral leaves. The "flossy" appearance from the leaf edges, together with the characteristic yellowish-brown or reddish-brown color make the genus easy to recognize.
Like Ptilidium, Blepharostoma and Trichocolea have deeply divided leaves with marginal cilia, however Ptilidium differs from these other two genera in that its leaf cells have bulging trigone
Trigone
The trigone is a smooth triangular region of the internal urinary bladder formed by the two ureteral orifices and the internal urethral orifice....
s (thickenings at the corners between 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).
The plants grow in dense mats, with stems growing either prostrate or ascending. Individual stems are once or twice pinnate
Pinnate
Pinnate is a term used to describe feather-like or multi-divided features arising from both sides of a common axis in plant or animal structures, and comes from the Latin word pinna meaning "feather", "wing", or "fin". A similar term is pectinate, which refers to a comb-like arrangement of parts...
, rarely with branches and only a few short 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. The leaves are incubous
Incubous
The term incubous is used to describe the way in which the leaves of a plant are attached to the stem. If you were to look down from above on a plant where the leaf attachment is incubous, the upper edge of each leaf would overlap the next higher leaf along the stem...
and divided deeply into three to five portions, and edges of the leaf divisions are fringed with cilia. The underleaves are similar to the lateral leaves, but are slightly smaller. All species are dioicous, producing antheridia
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 archegonia
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...
on separate plants. The archegonia are terminal on a main stem. Mature 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...
s develop from within a large perianth with three distal folds.
The three species in the genus may be distinguished by the density of cilia along the leaf margin, depth of lobing in the leaf, width of the leaf base, and the substrate on which it is found growing. P. californicum has few cilia along the edge of its leaves and has underleaves lobed to about seven-eighths of their length. The other two species have many marginal cilia and underleaves lobed to no more than half their length. P. ciliare usually grows on soil and has leaf lobes that are 15–20 cells wide at their base. P. pulcherrimum usually grows on wood or rock, and has leaf lobes normally 6–10 cells wide at their base.
Distribution
The genus Ptilidium has a borealTaiga
Taiga , also known as the boreal forest, is a biome characterized by coniferous forests.Taiga is the world's largest terrestrial biome. In North America it covers most of inland Canada and Alaska as well as parts of the extreme northern continental United States and is known as the Northwoods...
distribution, and is found in abundance in coniferous forests of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, as well as in 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...
and Tierra del Fuego
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of a main island Isla Grande de Tierra del Fuego divided between Chile and Argentina with an area of , and a group of smaller islands including Cape...
. Plants often grow attached to the bark of trees in the northern hemisphere, but may occur in rocks in mountain districts of New Zealand. At the more temperate ends of its range, plants are restricted to higher elevations.
Schuster (1984) proposed that the disjunct distribution of Ptilidium ciliare between the northern and southern hemispheres could be explained by migration of the Indian Plate from Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
. In this hypothesis, P. ciliare is a species originally native to Gondwana, and sterile populations existing in modern New Zealand and Tierra del Fuego are relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
s of this earlier distribution. The other two species of Ptilidium are thus believed to be later descendants. Schuster's hypothesis is partially based upon a belief that Ptilidium is related to the genera Mastigophora and Dendromastigophora, both of which are largely restricted to the southern hemisphere. However, this relationship is not supported by modern molecular analysis, which places Mastigophora in an entirely different part of the liverwort phylogeny. Instead, Ptilidium is now believed to be part of an isolated clade allied only to two East Asian endemics, and it is thus more likely that the sterile populations of Ptilidium in the southern hemisphere reflect long-distance dispersal of plant fragments. Ptilidium ciliare is tolerant of desiccation and is ubiquitous in the Arctic, but rarely produces 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, and it is therefore believed to spread by means of such fragments.
Phylogeny
The diagram at left summarizes a portion of a 2006 cladistic analysis
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...
of liverworts based upon three chloroplast genes, one nuclear gene, and one mitochondrial gene. The genus Trichocoleopsis was not included in the original broad analysis, but is the sister taxon of Neotrichocolea according to a more narrowly focussed study utilizing six chloroplast genes, two nuclear genes, and a mitochondrial gene.
The genus Ptilidium is sister to the Trichocoleopsis-Neotrichocolea clade. This combined clade, in turn, attaches at the base of a large clade (2600 species) designated "Leafy II". That clade, together with "Leafy I" (another 1800 species) and Pleurozia
Pleurozia
Pleurozia is the only genus of liverworts in the family Pleuroziaceae, which is classified within the order Jungermanniales. The genus includes eleven species, and as a whole is both physically distinctive and widely distributed...
constitute the Jungermanniales
Jungermanniales
Jungermanniales is the largest order of liverworts. They are distinctive among the liverworts for having thin leaf-like flaps on either side of the stem...
, as traditionally defined. Ptilidium, Neotrichocolea, and Trichocoleopsis thus sit at the base of the Jungermanniales, at a point where the two major groups of leafy liverworts diverge from each other.