Corallorhiza, a plant that eats fungi
Corallorhiza is a representative of the orchid family. The orchids are one of the largest families of flowering plants, a group with over 25,000 species. Although the genus Corallorhiza is restricted to North America, with roughly a dozen species, most members of the family are found in the tropics. Probably the most commonly seen orchid in the northeastern US is the pink lady slipper but there are another 10-15 species of orchids that relatively easy to find, although they never are abundant and many occur in restricted habitats, e.g. bogs. Corralorhiza is an unusual angiosperm because it is non-photosynthetic, a characteristic that is very rare within plants in general but does occur occasionally in several plant groups.
Taxonomy and Phylogeny
The orchid family is distinctive in a number of ways and its members are generally quite easy to recognize when in flower. They are in the monocot group, which is usually considered a class (remember that families are grouped into orders, orders into classes, and classes into phyla). Monocots are a monophyletic group that is thought to have diverged early (perhaps 130 million years ago) from the rest of the angiosperms. The remaining angiosperms (i.e. all flowering plants except monocots) do NOT form a phylogenic entity and hence modern treatments do not divide angiosperms into two groups (monocots and dicots) but into several groups, the two largest being monocots and ‘eudicots’, a group that includes most, but not all, of the old dicot members. Monocots have a number of features that distinguish them from other flowering plants: a single cotyledon in the seed, lack of secondary growth, flower parts typically in 3’ s, and stems with scattered vascular bundles.
Structure
Orchids are herbaceous perennial plants that have several distinct growth forms. Many orchids are epiphytes, plants growing on the trunks of other plants, and may have features including ‘aerial roots’ and ‘pseudobulbs’ which allow them to be successful under these conditions. Corallorhiza orchids do not have a typical orchid structure because they are non-photosynthetic and have very reduced/no leaves while most orchids have very visible leaves that may be stiff, oval and overlapping or sometimes may be grass-like. Many orchids produce rhizomes (horizontal stems running below ground), corms (short, fattened vertical stems) or tubers (enlarged stems that are not oriented vertically).
Reproduction
Most orchids exhibit sexual reproduction that is possible because of elaborate pollination mechanisms that most commonly involve bees or wasps. The flowers of orchids are unusual because pollen is not dispersed as individual grains but rather in large packets (‘pollinia’) that represent the the entire anther of an individual stamen and contain thousands of pollen grains. Seeds of orchids are extremely small, often less than 0.5 mm, sometimes less than 0.1 mm (less than 100 microns). This small size is possibl