figuring out inflorescences? need help

kate_rose(7a TX panhandle)January 18, 2007

Hi,

I am working an a computerized plant guide that translates

a key into laymens language. I have a biology background

but its in frogs not plants.

My confusion is this:

As I understand it there are inflorescences (non-simple ones) which are racemose (indeterminant so the older flowers usually appear at the base of the inflorescense) and those that are cymose (determinant so the older flowers appear at the top of the inflorescence). So far so good.

The confusion comes when I look at scorpoid and helicoid cymes. It would appear that the oldest flowers are at the base of the inflorescence yet these are classified as cymose. Of the examples I have looked at Phacelia stands out as appearing this way (its helicoid).

The only way it makes sense is if the first and oldest flower is considered the terminal one and all the others are coming off of one branch below it. It sure doesn't look this way though.

I looked at all the explanations on the web but there seems to be considerable confusion about the usage of the term

cyme (is it sometimes used casually to just describe the shape of the inflorescense??).

I apparently need to acquire a good botany text but I

haven't yet so please help me understand this if you can & recomend a good text if you know of one.

Thanks,

Kate

Thank you for reporting this comment. Undo
rhizo_1 (North AL) zone 7

There really isn't any confusion regarding the term 'cyme', but there are many interpretations (expressions) of this inflorescence. I would say that the one single unifying characteristic between all cymose inflorescences is that they are determinate. In some cases, that might not be observable but has to be learned. You've mentioned a couple of good examples of this.

Here is a link that might be useful: Try this one on for size

    Bookmark   January 18, 2007 at 2:40PM
Thank you for reporting this comment. Undo
The_Mohave__Kid(Nevada)

A useful book is "Plant Identification Terminology" by James G Harris and Melinda Woolf Harris.

Good Day ...

    Bookmark   January 18, 2007 at 8:17PM
Thank you for reporting this comment. Undo
kate_rose(7a TX panhandle)

Rhizo,

If I understand what you said there can be a cyme, helicoid or otherwise, which is completely morphologically indistinguishable from a raceme because there are no characters to differentiate the two (at least not unless you look on a developmental or cellular level). I mean none that could be seen with a hand lens. I read in the link you provided that in the helicoid cyme that the 2ndary floral axis arises from between the bracts of the "terminal" flower and continues in this pattern in some species. Is this a consistent character that could be used to distinguish the 2 or is this just a sort of exception to the rule that must be learned as you mentioned.

Mohave, I hope you had a good day too. Thank you for the reference.

Thank you both for the help.

K-

P.S. sorry about the mix up in terminology (red face)
for some reason my brain was reading determi"nant" instead of determi"nate"

    Bookmark   January 19, 2007 at 12:05AM
Thank you for reporting this comment. Undo
kate_rose(7a TX panhandle)

If anyone has input on the above I would really appreciate it.

Thanks,

Kate

    Bookmark   January 20, 2007 at 12:01PM
Thank you for reporting this comment. Undo
paalexan(NM)

"The only way it makes sense is if the first and oldest flower is considered the terminal one and all the others are coming off of one branch below it."

That's pretty much what's going on. You've got a stem that terminates in a flower; the first axillary bud below it then produces a new stem that contains one axillary bud and a terminal flower; the axillary bud of that stem produces yet another stem that contains another axillary bud & terminal flower; & so on & so forth.

You could get an apparently identical inflorescence via a secund, coiled raceme; but in this case, flowers would be arising from the axils of the bracts, whereas in a cyme you have new stems arising from the axils of the bracts.

That distinction falls apart, however, if your inflorescence has no bracts! & then we are left with either studies of development, or with inference; for instance, if you see a coiled inflorescence in Phacelia that can't be definitely identified as a cyme or a raceme, but you know that the closely-related genus Nama has open cymose inflorescences, it's a good bet that the coiled inflorescence in Phacelia is also cymose.

Patrick Alexander

    Bookmark   February 13, 2007 at 8:41PM
Sign Up to comment
More Discussions
reccomended plant science educational books to read
Hey everyone, looking for some plant science book recommendations...
zjharrison
Cold stratification & "tricking" seeds
Was originally posted here, in the Growing from Seed...
actionclaw
fyi, ubc botanical garden forums has a plant science forum
Plants: Science and Cultivation Disregard. Almost no...
albert_135
ok to grow an entire poplation of plants from one motherplant?
If i were to buy a single flowering, hardy pond plant,...
njbiology
What do you think about mycorrhizae fungi?
As a commercial product, I mean. Can it really help...
leaveswave
© 2015 Houzz Inc. Houzz® The new way to design your home™