The Orchidaceae

Few plants inspire passion like orchids do: we’ve been cultivating them for 3,000 years, despite the fact that they offer us little by way of food, clothing, medicine, or anything else people grow plants for.  In Europe orchid cultivation began about the time the Dutch tulip craze was waning, and now there are over 100,000 known cultivars and hybrids.

The number of species is impressive, too, estimated to be around 28,000 (some experts believe there may be as many as 35,000), in over 700 genera. This makes the Orchidaceae either the largest or second largest plant family (the other being Asteraceae), in terms of number of species. In both families the number of species is constantly changing, in accordance with both new discoveries and phylogenetic research.

In North America, there are 310 species of native orchids, making the Orchidaceae the 13th largest family on this continent*.

In Maryland, though, the news is sad. Although there are records for about 44 species (29 in the piedmont), of these…

  • 9 have been extirpated
  • 1 is a waif
  • 1 is alien
  • 12 are listed as endangered and/or S1 (highly state rare)
  • 1 is S1/S2 (highly state rare)
  • 4 are threatened and/or S2 (state rare)
  • 1 is S2/S3 (state rare)
  • 4 are vulnerable and/or S3 (watchlist)**

Orchids grow in almost every habitat, except in true deserts, open water, and glaciers***. Most of the species grow in tropical rainforests, but the family is cosmopolitan: orchids are found on every continent (and Oceania) except Antarctica.

They can be terrestrial or epiphytic. An epiphyte is a plant that grows on another plant for support, without causing the other plant harm (therefore not the same as a parasite). The epiphytic orchids have aerial roots that absorb water and nutrients from the air. They are mostly found in the tropics, while the terrestrial orchids are mostly found at higher lattitudes.

Terrestrial orchids grow with certain soil fungi in mutually beneficial associations termed mycorrhizae (singluar mycorrhiza). Because of this, our native terrestrial orchids are extremely hard to grow in the garden; if the correct fungi are not present in the soil, the orchid plants will likely die in a year or two, and seeds will not germinate.

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Orchids usually bear flowers on a spike, raceme, or panicle, or sometimes singly. A spike is a stem with single flowers along it (right); a raceme is a spike whose flowers have pedicels (below); and a panicle is a branched raceme.

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Although there is a huge variety of form, orchid flowers are easily recognized. They always have three sepals, which can be single or partly fused, and are either green or petal-colored; and three petals. Of the petals, the two lateral ones are usually identical, while the center one is formed into a lip or pouch. The flowers are usually bilaterally symmetrical.

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As for economic value, it’s entirely about the passion for ornamental flowers, with one exception: Vanilla planifolia, the only orchid species to produce an edible fruit. There are a few orchid species that produce edible tubers, but these have never been grown commercially.

next time: orchids in the Maryland piedmont


*BONAP
**Maryland Biodiversity Project
***Encyclopedia of Life

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