| Monotropoideae | |
|---|---|
 | |
| Monotropa uniflora | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Ericales |
| Family: | Ericaceae |
| Subfamily: | Monotropoideae Arn. (1832) |
| Tribes | |
| |
Monotropoideae, sometimes referred to as monotropes, [1] are a flowering plant subfamily in the family Ericaceae. Members of this subfamily are notable for their mycoheterotrophic and non-photosynthesizing or achlorophyllous characteristics.
The overall morphology of these plants is highly reduced compared to other members of the Ericaceae, which are practically all subshrubs, shrubs, or trees. By contrast, the Monotropoideae are all herbaceous perennials, in which an annual shoot reemerges seasonally (in spring or early summer, depending on climate) from a perennial root. The shoot can be characterized as a single inflorescence or cluster of inflorescences, and is generally a raceme with one to many flowers per axis, though occasionally the raceme may be so reduced as to appear similar to a spike, and in Monotropa , the inflorescence can take the form of a solitary flower. Notably, the shoots are achlorophyllous, in keeping with the mycoheterotrophic and non-photosynthetic nature of the plant, and the plants have a striking and distinctive appearance, with coloration ranging from pure white to pastel tones to very bright yellow or red. (If the Pyroleae are included, many of these species are partially photosythentic, and have green vegetative tissue, though leaves are usually reduced to a basal rosette.)[ citation needed ]
The emerging shoots may be erect or nodding, with erect or pendulous flowers, which may become more erect as the plant matures. The flowers themselves, in common with other members of the Ericaceae, have corollas that are generally bell- or cup-shaped, though the petals themselves may or may not be fused. However, the Monotropoideae lack the poricidal anthers that are characteristic of the majority of the Ericaceae. (The Pyroleae do have poricidal anthers, however.) Pollen grains are released as a monad, in contrast to the majority of the Ericaceae, which release pollen grains in tetrad groups. (The Pyroleae variously release pollen as monads, tetrads, or polyads.) Fruits are dry loculicidal dehiscent (or sometimes indehiscent) capsule or a berry. Seeds are highly reduced dust seeds. [2] [3] The shoot may or may not be persistent after seed dispersal. [4]
The monotropes were first described as a distinct plant family by Thomas Nuttall in 1818, when he united the Linnean genus Monotropa with his newly authored genus and species Pterospora andromedea as the family Monotropeae (changed by later authors to Monotropaceae when modern rules of naming plant taxa were developed). [2] David Don was the first to recognize this group as a tribe within the Ericaceae, later raised to subfamily status as the Monotropoideae by Asa Gray in 1878. [2] (However, George Arnott Walker-Arnott was the first to validly publish that name, as a subfamily of Monotropaceae, in 1832, hence, Arnott is cited as author of the name.) [5] [6]
Other classifications have included Monotropoideae as a subfamily of Hypopityaceae, by August W. Eichler (1875), and as a subfamily of Pyrolaceae by Carl Georg Oscar Drude (1889); both classifications united the monotropes with the pyrolids in a single group. Over the next century, authors have variously treated this group as a distinct family or as a subfamily of the Ericaceae, though the trend from Margaret W. Henderson (1919) onward was toward the latter subfamily classification, albeit, the influential Cronquist and Dahlgren systems continued to treat the group as the family Monotropaceae, separate from the Ericaceae. [2]
Contemporary molecular phylogenetics has clearly established the Monotropoideae as a group within the larger Ericaceae, though many of the details of relationships between the Monotropoideae and the rest of the Ericaceae are still (as of 2015) a topic of active research, particularly the question of whether or not the Pyroleae and the rest of the Monotropeae form a single monophyletic group. [7] [8] [9] [10] [11]
The species in this subfamily are all mycoheterotrophic, relying on fungal hosts for their carbon nutrition. The fungi parasitized by these plants are ectomycorrhizal species of fungi, that are part of the Russulaceae . Hence, these plants act as direct parasites of these fungi, and also indirectly, act as an epiparasite of conifers and the larger shared mycorrhizal network. [12] [13] [14] Monotropoideae species can generally be described as full, obligate mycoheterotrophs, though if the Pyroleae are treated as part of the Monotropoideae, include partially mycoheterotrophic (mixtotrophic) members as well. [13] [15] The parasitism by these plants is generally very specific in terms of its fungal hosts, ranging from single families of fungi, to a few closely related species. [12] [14] [16] [17]
The morphology of the root and the root-level fungal symbiont is distinctive and referred to as monotropoid mycorrhiza. [14] [18] [19] (Although mycorrhizas are generally considered to be mutualistic relationships, it is generally recognized that mutualism and parasitism exist on a continuum, and that plant-fungus symbioses with a clearly mycorrhizal root anatomy can include exploitative relationships.) [20]
The Monotropoideae are adapted for pollination by bumble bees ( Bombus ), including specialized buzz pollination in a few genera. In some genera (such as Monotropa ), some degree of self-pollination has been observed in addition to bumble bee pollination. [2] [21] Hummingbirds have also been observed visiting Sarcodes , though it is also primarily bumble bee-pollinated. [2] Several floral scent compounds of Monotropastrum humile , linalool, α-terpineol, and geraniol, have been demonstrated to be bumble bee attractants. [22]
Monotropoids occur in coniferous or mixed coniferous forests, often in areas with a heavy, closed overstory with low light availability. They occur in boggy areas, in deep humusy soils, and even relatively dry slopes. The soil pH in locations in which they occur is acidic to varying degrees. [2]
Distribution is through much of the temperate Northern Hemisphere, though ranging into the subarctic and montane tropical regions as well. [2] [23] Distribution is limited by available moisture (Monotropoideae species have limited ability to survive long enough to set seed during seasonal dry periods), [23] and by the distribution of conifer genera that are hosts of the specific host fungi these plants parasitize. [16] [23]
The distribution of Monotropa is responsible for the majority of the range of this subfamily, with other genera not having the same global distribution. The center of biodiversity for this subfamily is found in temperate western North America, along the northern and central California and Pacific Northwest coast and montane areas as far east as the Sierra Nevada-Cascade cordillera. Seven of the 10 genera usually recognized as members of this subfamily (excluding Pyroleae) occur there, with 6 of these occurring only in that region. [2]
The Ericales are a large and diverse order of dicotyledons. Species in this order have considerable commercial importance including for tea, persimmon, blueberry, kiwifruit, Brazil nuts, argan, cranberry, sapote, and azalea. The order includes trees, bushes, lianas, and herbaceous plants. Together with ordinary autophytic plants, the Ericales include chlorophyll-deficient mycoheterotrophic plants and carnivorous plants.
The Ericaceae are a family of flowering plants, commonly known as the heath or heather family, found most commonly in acidic and infertile growing conditions. The family is large, with about 4,250 known species spread across 124 genera, making it the 14th most species-rich family of flowering plants. The many well known and economically important members of the Ericaceae include the cranberry, blueberry, huckleberry, rhododendron, and various common heaths and heathers.
A mycorrhiza is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, the plant root system and its surroundings. Mycorrhizae play important roles in plant nutrition, soil biology, and soil chemistry.
The Russulaceae are a diverse family of fungi in the order Russulales, with roughly 1,900 known species and a worldwide distribution. They comprise the brittlegills and the milk-caps, well-known mushroom-forming fungi that include some edible species. These gilled mushrooms are characterised by the brittle flesh of their fruitbodies.
An arbuscular mycorrhiza (AM) is a type of mycorrhiza in which the symbiont fungus penetrates the cortical cells of the roots of a vascular plant forming arbuscules. Arbuscular mycorrhiza is a type of endomycorrhiza along with ericoid mycorrhiza and orchid mycorrhiza. They are characterized by the formation of unique tree-like structures, the arbuscules. In addition, globular storage structures called vesicles are often encountered.
Pterospora, commonly known as pinedrops, woodland pinedrops, Albany beechdrops, or giant bird's nest, is a North American genus in the subfamily Monotropoideae of the heath family, and includes only the species Pterospora andromedea. It grows as a mycoheterotroph in coniferous or mixed forests. It is widespread across much of Canada as well as the western and northeastern United States to Mexico. Along with Monotropa it is one of the more frequently encountered genera of the Monotropoideae.
Monotropa uniflora, also known as ghost plant, ghost pipe, or Indian pipe, is an herbaceous, parasitic, non-photosynthesizing, perennial flowering plant native to temperate regions of Asia, North America, and northern South America, but with large gaps between areas. The plant is waxy white, but some specimens have been described as having black flecks or pale pink coloration. Rare variants may have a deep red color. The name "Monotropa" is Greek for "one turn" and "uniflora" is Latin for "one flowered" as there is one sharply curved stem for each single flower. M.uniflora is commonly found growing in clumps of 2 or more, with its fungal source nearby.
Monotropa hypopitys, the so-called Dutchman's pipe, false beech-drops, pinesap, or yellow bird's-nest, is a herbaceous perennial plant, formerly classified in the families Monotropaceae or Pyrolaceae, but now included within the subfamily Monotropoideae of the family Ericaceae. It is native to temperate regions of the Northern Hemisphere, and is scarce or rare in many areas. However, it is still the most widespread member of the subfamily. While currently included in the genus Monotropa, recent genetic evidence strongly suggests that Monotropa hypopitys should be placed in its own genus, Hypopitys, with the single species Hypopitys monotropa Crantz, but possibly containing several other species.
Ophrys insectifera, the fly orchid, is a species of orchid and the type species of the genus Ophrys. It is remarkable as an example of the use of sexually deceptive pollination and floral mimicry, as well as a highly selective and highly evolved plant–pollinator relationship.
Corsiaceae is a family of monocotyledonous flowering plants. The APG II system (2003) treats the family in the order Liliales, in the clade monocots. This is a slight change from the APG system, of 1998, which left the family unplaced as to order, but did assign it also to the monocots.
Myco-heterotrophy is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph is the parasitic plant partner in this relationship. Myco-heterotrophy is considered a kind of cheating relationship and myco-heterotrophs are sometimes informally referred to as "mycorrhizal cheaters". This relationship is sometimes referred to as mycotrophy, though this term is also used for plants that engage in mutualistic mycorrhizal relationships.
The ericoid mycorrhiza is a mutualistic relationship formed between members of the plant family Ericaceae and several lineages of mycorrhizal fungi. This symbiosis represents an important adaptation to acidic and nutrient poor soils that species in the Ericaceae typically inhabit, including boreal forests, bogs, and heathlands. Molecular clock estimates suggest that the symbiosis originated approximately 140 million years ago.
Arachnitis uniflora, the sole species in the genus Arachnitis, is a non-photosynthetic plant species in the family Corsiaceae. This species is mycoheterotrophic, and it obtains carbon from mycorrhizal fungi of the family Glomeraceae which are associated to its roots.
Cheilotheca is a small genus of myco-heterotrophic plants in the family (Ericaceae). As currently circumscribed the group includes three species.
An ectomycorrhiza is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobiont, and the roots of various plant species. The mycobiont is often from the phyla Basidiomycota and Ascomycota, and more rarely from the Zygomycota. Ectomycorrhizas form on the roots of around 2% of plant species, usually woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families. Research on ectomycorrhizas is increasingly important in areas such as ecosystem management and restoration, forestry and agriculture.
The Arbutoideae are a subfamily in the plant family Ericaceae. Phylogenetic analysis supported all genera of the subfamily as monophyletic, except Arbutus. Moreover, it was suggested that the non-sister relationship between Mediterranean and North American species may be explained by a once widespread distribution in the Northern hemisphere before the Neogene.
Orchid mycorrhizae are endomycorrhizal fungi which develop symbiotic relationships with the roots and seeds of plants of the family Orchidaceae. Nearly all orchids are myco-heterotrophic at some point in their life cycle. Orchid mycorrhizae are critically important during orchid germination, as an orchid seed has virtually no energy reserve and obtains its carbon from the fungal symbiont.
Rhizopogon amylopogon is a sub-genus of Rhizopogon containing seven species.
Rhizopogon salebrosus is a mushroom species within the Rhizopogon subgenus Amylopogon. R.salebrosus is a monotropoid mycorrhiza that is of vital importance to the ecology of conifer forests, especially in the Pacific Northwest region of North America. Although it is native to North America, R. salebrosus has been found in Europe and its range is generally limited to mountainous regions with sufficient precipitation. The mycoheterotrophic plant, Pterospora andromedea is often found in an obligate association with R. salebrosus in western parts of the U.S. Eastern populations of P. andromedea are typically symbiotic with another Rhizopogon sub species, R. kretzerae.
Mucoromycota is a division within the kingdom fungi. It includes a diverse group of various molds, including the common bread molds Mucor and Rhizopus. It is a sister phylum to Dikarya.
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