scientific defining feature of orchidaceae?
 

in short, what makes an orchid an orchid. im not looking for the typical answers like "most orchids have seeds that dont have nutrients" or " orchid's pistils and stamens are fusd" but im looking for the scientific calssification, IE, what conditions the plant must meet to be classified as an orchid.... thanks!

im also looking for the same type of thing for the genus phalaenopsis, thanks!

thanks! thats exactly what im looking for!!!

does anyone know about for phalaenopsis?

thanks a million! what book is it? ill have to look for it!

Annoyingly, although I didn't try very hard, I couldn't find a formal definition. It's probably spirited away in academic books, or one of those things that's so obvious when you're a botanist you don't bother to write it down. :D
Wikipedia suggests, along with some of the characters mentioned:
Orchids are easily distinguished from other plants, as they share some very evident apomorphies. Among these are: bilateral symmetry (zygomorphism), many resupinate flowers, a nearly always highly modified petal (labellum), fused stamens and carpels, and extremely small seeds.

I'm pretty sure the number one feature is the column (gynostegium).

As for phalaenopsis, this site is ludicrously full of information, but this doesn't seem to cover the distinction between Phalaenopsis and other orchids, although one generally "knows one when one sees one!"; most orchids are distinguished based on flower features.

I bet this book has a formal description of the genus, but annoyingly, the relevant parts are not part of the Amazon preview!

---------- Post added at 11:50 AM ---------- Previous post was at 11:41 AM ----------

This paper is also quite interesting, if somewhat old.

I can't seem to find a single scientific description of the family of orchidacae. But below is the ones i could find for phalaenopsis.

According to Jay's (www.orchidspecies.com):
Phalaenopsis: It is monopodial with large succulent, drooping leaves with short stems, giving rise off the stem from among the leaves to an inflorescence which can have a few to a hundred flowers with a distinct 3-lobed clawed lip. The parts of the Phalaenopsis flower are, column {#1}, lateral lobe of labellum {#2}, mid lobe of the labellum {#3}, labellum {#4}, dorsal sepal {#5}, petals {#6}, lateral sepal {#7}

The type species is: Phalaenopsis amabilis which is defined as: This is a medium sized, hot to warm growing, robust, epiphytic native of northern Australia, Indonesia, Papua & New Guinea, the Philippines and New Britain occuring at elevations up to 600 meters in rainforests on trunks and branches overhanging rivers, swamps and streams with a short, pendulous, robust stem enveloped by imbricating leaf bases and carrying 3 to 5 fleshy or coriaceous, arcuate, pendant, ovate-elliptic, obovate to oblong-oblanceolate, obtuse to subacute, shiny green leaves that blooms on a slender, to 3' [90 cm] long, racemose or panicualte, laxly few to many flowered inflorescence that has small scarious, triangular bracts and color and size variable, fragrant, showy, long-lasting flowers occuring in the spring through summer. It recieves more light than the average Phal. You can tell if it is receiving the proper light levels if the leaves have a slight reddish cast. (Internet Orchid Species Photo Encyclopedia)

Another sources lists the description for subtribe Epidendroideae (of which Phalaenopsis belongs) as:
"Pollinia 2 t o 8 , h a r d , w a x y ; a n t h e r usually c a d u c o u s ; leaves various, o f t e n a r t i c u l a t e ;
h a b i t of g r o w t h various and A n t h e r t e rmi n a l a n d o p e r c u l a t e ( i n c u m b e n t ) o r r a r e l y e r e c t , u s u a l l y mo r e o r less
versatile; stems o f t e n w i t h c o rms o r c o rm- l i k e t h i c k e n i n g s .." (http://www.orquidarioilhadodesterro....6dd3fb3339.pdf)

Rather than try to understand and regurgitate the information, I would direct you to two taxonomic treatments of the genus:
The Genus Palaenopsis, Sweet, 1980, The Orchid Digest Inc.
Phalaenopsis, a Monograph, Christenson, 2001, Timber Press

thanks everyone! im at school now, but ill read up later.

this is for a research paper, so i want to be able to state scientific definitions :)

i cant figure out how to get a hold of Christenson's Phalaenopsis, a Monograph

they dont have it at any libraries, i searched the whole system.