This is a confusing genus, and trying to ID one from a single pic can be daunting. C. communis is easy to ID with a clear flower macro because the little yellow things in the middle of the flower have brown dots. It has 2 blue petals and 1 lesser petal that's sometimes referred to as clear but can be opaquely bluish or white. It comes to a point.

The size of the blooms varies greatly, which I never realized until seeing several types in person. Pics w/o scale are more difficult.

Some description keys, pics:
communis: http://www.illinoiswildflowers...
diffusa: http://keys.trin.org.au/key-se...
erecta: http://www.wildflower.org/plan...
benghalensis: http://www.gri.msstate.edu/ipa...
virginica: http://www.wildflower.org/plan...

There are others.

The following blooms do not fit with C. communis but have been placed in that entry in the database here. Please place any comments about the specific pics on the individual discussions.

The thread "Doubt C. communis" in Photo of Dayflower (Commelina)
The thread "Not C. communis" in Photo of Virginia Day-Flower (Commelina virginica)
The thread "Doubt C. communis" in Photo of Asiatic Dayflower (Commelina communis)
The thread "Doubt C. communis" in Photo of Asiatic Dayflower (Commelina communis)
The thread "Not C. communis" in Photo of Dayflower (Commelina)

Thanks!

Flora of North America says the "antherodes yellow sometimes with central maroon spot". The key here is SOMETIMES, not always. One important key that can't be seen in the any of the photos is the spathes. If that were visible it would be easy to be sure because there are only three species is North America that have distinct bases, C. communis, C. caroliniana and C. diffusa.
Since it is not possible we have to look at other clues.

The photo one shows distinctive dark green stripes on the spathe which is indicative of C. communis, so ID is probably correct.


Photo two shows no distinct stripes on spathe plus it has a larger proximal petal that is nearly the same color as the distal petals so not likely C. communis. It looks to me more like C. virginica. piksihk who contributed the photo lives in a county where C. virginica grows so that would be my best guess without actually having the plant in hand.


Photo three and four, I have no guess. Other than the lack of maroon spot there is not enough visible to make any guess.


Photo five, JonnaSudenius is not in North America, but the fact that it has three equal size large blue petals indicates that it is not C. communis which has a very reduce proximal petal that is lighter than the distal petals. This is the quote from FNA for C. communis, " proximal petal paler or white, very reduced, distal petals blue to bluish purple".

TY so much for your comment & efforts!

I agree with your assessments but am unsure about the first in that after removing the maroon/brown spots from consideration if not required, the 3rd petal isn't pointed and much too blue, color of top petals too pale, and highly ruffled petals are anomalous. None of which may be considered diagnostic, IDK. Is there a hierarchy of characteristics, like striped spathes are more diagnostic than petals?

The proximal petal looks white to me. If you enlarge the photo you will see that some of the flower parts overlap the petal and are out of focus and the blurr gives it a blueish tint. I saw nothing, other than the photo in the link you gave that indicates a pointed petal. It could be a variation or an illusion cause by curling. I seen plenty of photos online that show a rounded petal. That said, I did some more search and although I find nothing in literature that say C. erecta has striped spathes, I have seen photos showing stripes (assuming that they were accurately identified) so that's a possibility. Also look at the photo again I notice that the leaves are very long and narrow compared to most C. communis photos I see online. So there is definitely room for doubt in that photo also, it very well be C. erecta. But that brings us back to the same problem of not enough info. There is enough to raise doubt to the ID, but not enough to make a positive ID. As far as hierarchy is concerned I don't know of any. Understanding that plants can be variable, you have to take the info as a whole not just bit and pieces that these photos present.

Thanks for your input! If I can find again the passage I read a while back about the 3rd petal, I'll put a link here. If my old bifocaled old eyes are seeing something that nobody else does, that's good to know and would be good cause to disregard.

The parent plant entry is a perfect solution only available here on NGA for great but questionable pics until/unless an agreement can be reached about what (other) species they are. In this case, those on which everyone agrees are definitely Commelina but not C. communis, species unknown. If others agree that some of the pics can't be confirmed as C. communis, I would support moving to parent if opinions are being considered.

I found 3 excellent descriptions of C. communis:

http://www.iowaplants.com/flor...
https://anps.org/2015/09/18/kn...

And this one explains interestingly, "The genus name Commelina recognizes the work of Dutch botanists Johan and Caspar Commelin, brothers represented by the two large blue petals; in a sort of botanical cruelty joke, a third brother who made no scientific contributions is memorialized by the dayflower's insignificant third petal."
http://www.hiltonpond.org/This...

at the insignificant brother!

I've never put any photos in the database, but here is one that shows a lot of the plant but limited closeup of the blooms. I just consider it generic Commelina.

LOVE that pic!

The brother is memorable!