What is it? Kalanchoe luciae or K. thyrsiflora? US National Arboretum, Washington DC

The only way to really know for sure is to see the flowers. K. luciae flowers white while the other species flowers yellow (sometimes gray-green). The leaves are not necessarily all that different, vegetatively the plants tend to be extremely similar. K. luciae will branch more often and earlier, especially the forms in cultivation.

Until very recently luciae was vastly more common in cultivation than the other species, which was essentially only found in botanical gardens or hard core specialist collections. But I saw thyrsiflora was recently (last year or two) being produced in numbers, and this simple distinction is likely to be less and less useful over time.

Regardless, when in doubt, guess luciae. Based on sheer numbers, you will most likely be right.

More info about those species here:

https://www.smgrowers.com/info...

@Baja_Costero and @Nick_Kurzenko They look similiar to mine which send up huge stalks that have white blooms. The redness is more prevalent when they are stressed.
Today this is what they look like and to horrify myself into cleaning it up. Lol



Yes the blooms will tell you. My stalks are dried up and I removed some but this is what they look like today. Just a fyi to give you a heads up.

Thank you very very much

According the USNA database there are no Kalanchoe luciae, no K. thyrsiflora in Arboretum collection. But the collection include 1 Kalanchoe tetraphylla. The name Kalanchoe tetraphylla has been treated by many online sources as a synonym of K. thyrsiflora.
https://worldofsucculents.com/...
Therefore, I think now that in my images it is more K. thyrsiflora than Kalanchoe luciae.

The name K. tetraphylla is almost certainly an error... in reality it is very different from the other two species. It has much fewer leaves and flowers laterally, not terminally. That web site (WoS) is not an authority on anything and more likely to be wrong than many other succulent sites, and I would recommend consulting it last to resolve naming issues. More info on the species K. tetraphylla here.

https://www.smgrowers.com/info...

The images at the link show leaves with scalloped edges.

Thank you. Now I know that K. tetraphylla and K. thyrsiflora are different species. And now I know exactly that my images are K. thyrsiflora! I found in my collection old pictures with the same plant from USNA with label K. thyrsiflora. In USNA database this plant named as K. tetraphylla, but real plant has label K. thyrsiflora. Thank you so much again.

Yes, Tiffany is right, tetraphylla has somewhat hairy leaves with scalloped edges.

Despite the tag, I would still think the plant is much more likely to be luciae.

I am completely confused. But I will adhere to your point of view, since you are the best expert I know.
And thank you.

It probably depends on when the tag was made.

The San Marcos Growers article says, "In another bit of horticultural confusion, the plant long grown in the California succulent trade under the name of Kalanchoe thyrsiflora is actually the closely related Kalanchoe luciae. First described in 1908 by Raymond Hamet, the specific epitet is to honor a Lucy Dufour. In March-April 2001 issue of the Cactus and Succulent Journal this confusion of names is discussed in an article by John Trager with a picture of the true Kalanchoe thyrsiflora. The article notes that:

"The plant commonly distributed under this name [Kalanchoe thyrsiflora], sometimes with the whimsical common name - coined by one enterprising nurseryman - of "flipping flapjacks" is in fact the related K. luciae ssp. luciae. Both species bear the fleshy, paddle-like, obovate leaves to which the common name refers. Those of K. luciae blush deep red, especially with cool winter temperatures. Those of K. thyrsiflora are more uniform chalky green or white, covered with a thick flour-like coating of wax. The flowers of the two species also differ. Those of K. luciae are not strongly scented and have an urnceolate flower tube with pale-yellow lanceolate corolla lobes. Those of K. thyrsiflora are heavily sweet scented with a cylindric flower tube and brilliant yellow broadly obovate lobes."

FWIW, the WOS page for K. thyrsiflora is more strong on the issue. Can't copy the text to paste.
https://worldofsucculents.com/...

But everyone seems to agree it's one or the other. You'll know for sure when it blooms. It looks extremely happy & healthy, so there's no reason it wouldn't bloom sometime in the next year or two. Let us know what you get!

Thank you for your valuable notes, Tiffany. I'll try to look at blooming plant, if it will be possible.

They are not my notes, but I'm happy to share the info. : )

Is it your plant or one you saw @ USNA? If it was at the public garden, they have a plant finder:
https://usna.usda.gov/abe/

It says:
Kalanchoe tetraphylla
paddle plant, paddle kalanchoe
cactus/succulent
Kalanchoe thyrsiflora
Crassulaceae
82462-H
cultivated origin
Introduction Garden - Container Plants (public display May-October only)

That fits the profile of an incorrectly labeled K. luciae plant.

Nick, thank you for the vote of confidence but I am no kind of expert. This subject keeps coming up over and over again, so it's a common point of confusion. I guess any time two plants can't be easily distinguished without seeing the flowers, there's bound to be plenty of mixups between them. At this point it seems like we're still doing damage control for past mixups made by databases and taxonomic authorities, but at least the record is straight for people who are patient enough to see their plants bloom.