Left/right and right/left petals?

[tropterrarium]

Which petal on an orchid flower is the left, which one the right?
If you look at it face on left is left, right is right?
Or in growing direction, so when you look at it, left is right, and right is left?
It is the same question as with the human heart, it is on the left side from the perspective of the person, but on "right" from the perspective of an external viewer facing the subject.

I sort of suspect it is in viewing direction, and in natural orientation, i.e., with lip down (in most cases, though there are exceptions, of course). Otherwise we add the further complication of resupination. That fits with the notation of "dorsal sepal" opposite the lip, which starts pre-resupination in ventral position.

This is not about correct vs. incorrect terminology, but rather what the generally accepted standard is. Any references would be greatly appreciated.

Thanks for your wisdom!

[WhiteRabbit]

I don't know if there is a correct, or accepted perspective To me, at least, it would seem logical to use one's own left or right, if there is a need to specify, as the plant really has no left or right of its own.

If I am mistaken, I'm sure someone will correct me

[tropterrarium]

Hi Sonya,

thanks for taking a first stab. Left-right are certainly human constructs, but they help in communication. I try to come up with figure caption and description for a rare preserved flower with strange flower structure, where one of the petals was broken off. So that's the background for my inquiry.

Extrapolating from us humans as Bilateria, there are some parallels in orchid flowers, which are also bilaterally symmetrical = zygomorphic. The dorsal sepal gives us one axis. By analogy, front-back (anterior posterior in general zoology, [but in medicine anterior-posterior = ventral-dorsal, where zoological anterior-posterior is cranial-caudal]) axis.

If a strict parallel to zoology is made, then anterior would be towards the viewer (we look at the face of the orchid flower), and posterior, would be away from the flower towards the flower spike. If that is the case, then what we see on the right, is flower-anatomically on the left, so same reversal as in human heart when two people face each other.

I just wonder whether this strict anatomically correct approach is used in the real world.

[WhiteRabbit]

Interesting! I can understand your looking for clarification in such a circumstance! I hope that someone with more knowledge than I in this regard can give a definitive answer!

If you are unable to get a definitive answer, perhaps in the description you could state "on the viewer's / observer's left (or right)" ?

[tropterrarium]

OK, checked with some old pro botany pals.

For "normal" orchids, i.e. those that resupinate, the lip develops dorsally, but post resupination if ventral. The median sepal then is dorsal (aka dorsal sepal). The anterior-posterior axis is running parallel to the pedicel-ovary. Then with lip down, viewing the face of the flower, the right tepals are on the left side, the left tepals on the right. This is apparently how it is most often referred to.

In non-resupinate flowers, the lip remains dorsal, the median sepal is ventral, so if we have the dorsal lip up, then right tepals are on the left, left on the right.

In orchids with non-resupinate flowers but pendent spike, the lip remains anatomically dorsal, but is at the bottom, the median sepal is anatomically ventral but at the top, the right tepals are on the right side, the left on the left side.

So the left-right orientation is technically reversed in resupinate and non-resupinate flowers when lip is facing the same direction (down). Because this is a bit too weird for everyday usage, the lip is down, and all the tepals on the right are referred to as "left" and vice versa, i.e., the left-right nomenclature for resupinate flowers is employed for all orchid flowers.

How a simple question can derail into something waaay too complicated!

Bottom line, a labeled drawing in the introduction solves all ambiguities.

[WhiteRabbit]

Thanks for the info! I'm glad you found the answer!