Flowers of Aristolochia arborea
It is always intriguing to find the outlier in a plant family. As noted in the Angiosperm Phylogeny Group summary, the Aristolochiaceae, or birthwort family, “…are more or less herbaceous plants (they are quite often vines)”. The epithet arborea, though, reveals the habit of this species: a (small) tree.
I imagine if I had first seen this in person, my reaction would have been similar to Matt’s initial bewilderment, as documented on the In Defense of Plants weblog. No matter how much one thinks one might know, there is always room to learn more.
There are 500 or so species of Aristolochia, with most species either found in the tropics or subtropics. Only a few are shrub or tree-like. Aristolochia arborea is native to moist mountainsides of El Salvador, Guatemala, and adjacent Mexico.
In Revision of the North and Central American Hexandrous Species of Aristolochia (Aristolochiaceae), the author notes that a collector (Broadway) had described the flowers as “[resembling] bats clinging to the plant on old wood”. Others (including Matt above) have been struck by the appearance as being similar to mushrooms. This resemblance is also present in the floral scent (like fungi) and where the flowers are borne on the tree (near the ground). Apparently, the mimicking even occurs at the microscopic level. The Botanischer Garten München-Nymphenburg reveals why (deceiving pollinators) in their audioguide tour: Aristolochia arborea.
Botany / photography resource link: the fungi photographs of Bernd Rügemer. Spectacular, and brought to our attention by one of the UBC Botanical Garden fungi forum participants, allelopath, in this thread.
Wow, that’s wild!
So, I’ll admit it is slightly stranger than the other Aristolochias but they are all weird.
It is always worth mentioning that no Aristolochia should ever be eaten as they are carcinogenic and liver toxic. Quite a few species have been used in traditional medicine in Europe, the Americas and Asia but they should never be used at any dose. The name birthwort comes from one of the old uses. Some were even included in bitters for making cocktails.
The toxins are variations on aristolochic acid, an unusual nitro-substituted alkaloid.
Another unusual feature is that each seed has an elaiosome (oil-body) attached that is larger than the seed itself. This blob of food encourages ants to disperse the seeds when the fruit falls apart on the ground.
German text with pictures: http://www.botgart.uni-bonn.de/o_haus/aristo03.html
English version without pictures: http://florawww.eeb.uconn.edu/reference/arisarbe.htm
A paper from Heidelberg in 2016 reports that this species does have nectaries to feed the visiting pollinators. Perhaps only a small amount of nectar is produced, to stop the insects starving before they pass on the pollen at another fungoid flower. This paper also has a photo of a dissection of the flower showing the internal structure. https://www.researchgate.net/profile/Claudia_Erbar/publication/309517739_Nectaries_in_fly-deceptive_pitcher-trap_blossoms_of_Aristolochia/links/5a0057864585159634b7449e/Nectaries-in-fly-deceptive-pitcher-trap-blossoms-of-Aristolochia.pdf
Though some parts of the fragrance have been identified the mushroomy parts have not yet been characterised.
The original description from 1858 does not seem to be online but we can see the plate and description in Curtis’s Botanical Magazine from 1862. https://www.biodiversitylibrary.org/page/432319#page/22/mode/1up
Over 30 years later in 1895 a French author was expressing surprise. “Une Aristoloche en arbre!” https://www.biodiversitylibrary.org/page/49796047#page/44/mode/1up
I remember seeing a small plant of A. arborea at Fairchild Garden and it had kind of shiny leaves with decorative prominent yellow veins. In the vine pergola there was a large Aristolochia maxima with large clusters of small cauliflorous flowers that even occurred at ground level. Since then the vine pergola has been rebuilt and paved and I don’t know if it’s still there. It was a large woody trunked vine. Our winters have been getting milder but it may still occasionally get cold enough to kill plants that can’t take dew points under 40 degrees F which probably includes A. arborea.
so interesting and beautiful, thank you, Daniel
Wow….I have never seen anything like this before. Fascinating ! Thanks.
Wow. That is pretty amazing.
Many, many thanks for yet another wonderful botanical adventure.
And, thanks to the other folks who chimed in with so much more fascinating info.
You blew my mind, a little…in a good way.
😀
Always intriguing to learn another species. This one was fascinating. I did not see this A. arborea at Fairchild this past February.
In TN. We have two vines. I have found one on our VECA walking trail in Memphis and am waiting on bloom for positive I.D. Love the high function of this native. Suzy Askew
An outlier for sure – thank you!