What makes an Orchid an Orchid

[RosieC]

Ok, this is a question that friends keep asking when I say I have this new Orchid hobby and I don't have a clue what the answer is.

It seems like a fundamental question so I feel embarised that I don't know

What makes an Orchid an Orchid?

For example why is a Plurothallis an Orchid but a Dandelion is not?

What is the common factor that links them all together

With many of the genera I can look at the flowers and say "that's an orchid". Recently on a visit to a botanical gardens and while in the 'orchid room' I looked at some of the things my husband pointed out and said "No way is that an orchid, looks more like a bromiliad" and sure enough we had that confirmed.

But I can't do that with all the Genera and I don't even know what it is about them that I am identifying even when I can spot them.

So... does any one know the proper definition of what links them together. I would love to know.

[camille1585]

Sounds like a question from my botany classes a few years back! A lot of plants are classified according to flower morphology or unique caracteristics. The dandelion is a member of the Asteracea, the daisy family, because it is composed of many small flowers. On daisies there are two types of flowers, the small yellow ones in the center and the more flashy outer ones with an extra flower part.
Orchids also have unique characteristics. They have seeds with no albumen (reserves). The lower tepal is transformed into a lip (with varying shaped and sizes depending on the species). The stamen are always fused to the style, forming the column. Also, the flowers are always zygomorphic, meaning that thet have an axe of symetry
Another interesting fact, it's the largest family of flowering plants!

That's what I know, there are probably other criteria!

[Phantasm]

I find the key characteristic is in the flower parts; 3 sepals and 3 petals. These parts are sometimes fused as with masdevallias that have fused sepals, or petals that are modified into a lip, or more complicated arrangements as in Stanhopea.

[cabnc]

To be called an "orchid', a flower must have:
1. Bilateral symmetry (zygomorphic)
2. A gynandrium (column)
3. A rostellum
4. Pollinia
5. A labellum (lip)
6. Seeds without endosperm

[Jerry Delaney]

A real bonus for us trying to grow them is that they do not form a permanent main root system. It is also one of the few plants that have both colored sepals and petals. Everyone mentions the fusion of male and female reproductive parts into a column. To my (minimal) knowledge, there is only one non orchid with this arrangement and that is the common milkweed. I often wonder if that is true?

[RosieC]

Thanks everyone, it's great to finally know what it is about them that makes them orchids.

[kiki-do]

Good question Rosie, I too get confused about what makes an orchid, an orchid. Thanks for asking so I could get an answer also.

[camille1585]

Originally Posted by Jerry Delaney

A real bonus for us trying to grow them is that they do not form a permanent main root system.

What do you mean by that?

[RosieC]

I've also just gone through and looked up all the big words, so now I think I've got it straight in my head

[Royal]

As Phantasm stated, floral formulas are great indicators to distinguish plant families. That still leaves us with the entire lily family, but it will distinguish it from Bromeliaceae.

There are ALWAYS exceptions in nature, but for the most part, cabnc nailed it. I'd just change "must" to "usually". In one group there 's not a real column as we know it because fusion of the stamen filaments to the style isn't complete. Also some seed does contain small amounts of endosperm. See, not all orchids play by the same set of rules.

My point is, you got some good answers to be able to recognize characteristics of orchids, but nature seldom gives us absolutes - especially when humans created the taxonomic systems.