Dear Readers, I was so taken by the Indian Bean Tree (Catalpa bignoniodes) that I found growing in St Olave’s Court in the City of London last week that I thought I’d investigate a bit further. This is a magnificent street tree, with its enormous leaves, striking bean pods and extraordinary flowers, and you may sometimes see the golden-leaved cultivar ‘Aurea’, which adds another element to the tree’s attractiveness with its lemon-hued foliage. It is such an unusual plant that I can’t believe I’ve never paid it any attention before. Apparently the bean pods are sometimes used by children as a sword/light sabre substitute, and I can see why.
Indian bean trees, or catalpas, come originally from the southern states of the US, and one of their alternative names is ‘cigar tree’. The photo above shows why. The name ‘catalpa’ might derive from the Muskogee word ‘kutuhlpa’, which means ‘winged head’ – inside the beans are winged seeds which will spin away in a breeze to find a new growing site. Once landed, the trees seem to have a habit of spiralling towards the light, leading to some very eccentric growth patterns. I noted last week that the tree that I saw seemed to be determined to reach the small window of sunshine between the buildings that surrounded it, and some other images show the same determination.
The main reason for planting this tree is, however, for its flowers. Goodness. They appear in July, and I shall have to put a date in the diary to remember to go and look. If I told you that one of the closer relatives of the catalpas is the house plant incarvillea, I’m sure you wouldn’t be surprised. The first Indian bean tree is said to have arrived in the UK in the eighteenth century, brought here by Mark Catesby, who published the first ever guide to the natural history of the Americas between 1729 and 1747.But what really intrigues me about the Indian bean tree is that, most unusually, it produces nectar in its leaves. I mentioned this in my original post, but something about it had me scratching my head. Producing nectar is expensive for a plant, which is why it is usually a way of attracting insects for pollination, so why would this tree ooze sugar from the veins in its foliage? I had to dig a bit, but a reason finally appeared.
The Indian bean tree’s leaves are the only food of the caterpillar of the catalpa sphinx moth (Ceratomia catalpae). The larvae can completely strip a tree of its leaves, sometimes several times per year. It can be so damaging that the first ever trial of aerial crop dusting was an attempt in 1921 to get rid of the caterpillars from a catalpa farm. The jury seems to be out as to whether the insects actually cause long-term harm to the tree, with some people arguing that the frass from the larvae is such a good fertilizer that on balance the Indian bean tree is not harmed, and others saying that they regularly give their tree a good hose down to stop the worst depredations of the ‘catawpa worm’.
However, the tree is not without help. Enter the bodyguard ant (Forelius pruinosus). A 2003 study by J.Ness showed that when the caterpillars attacked a catalpa, it started to produce the nectar from its leaves. This in turn attracted the ants who not only enjoyed the sweet treat, but turned their attentions to the caterpillars. Hence, the depredations of the moth were not as bad as they might have been. When in balance, nature seems to have an answer for everything.
Incidentally, the caterpillars are a great favourite as bait for anglers, and in some parts of the US catalpa trees are planted just so that the ‘worms’ can be harvested and used to catch catfish.
Fortunately in the UK we don’t (yet) have the catalpa sphinx hawkmoth, so I think those lovely big leaves are safe for the moment.
The wood of the Indian bean tree was once used for fencing and for furniture making. The tree is sometimes now planted in areas of soil erosion, because the roots can help to hold the soil together, and historically the tree was often planted as a shade tree, close to the house. The huge leaves provide shelter and shade for birds too, although I’m not sure how far they eat those catalpa caterpillars – the tree produces a chemical which will deter most herbivores, and these substances are often bitter and unpleasant, so maybe the caterpillars don’t taste so good.
The beans and bark have been used as a cough medicine and to reduce the symptoms of asthma, and a distillation of the fruit has been used as a cure for conjunctivitis. The roots, however, are very poisonous.
And now, a poem. While the Indian bean tree is very beautiful, many US websites also describe it as what might politely be called ‘a pain in the backside’. The flowers drop off and turn to mush, the beans do the same, occasionally whole branches crack and hang, the leaves are either eaten by catalpa worms or fall and make the paths slippery. And yet. John Ciardi (1916-1986) seems to sum up the dilemma in his poem ‘The Catalpa’, which is not just a consideration of this tree, but of what price we put on the beauty of a moment.
Photo One by geograph-5810580-by-Jaggery
Photo Two by By Jean-Pol GRANDMONT – travail personnel, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3633275
Photo Three by By Le.Loup.Gris – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15730180
Photo Four by Epibase [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
Photo Five by By Patrick Coin (Patrick Coin) – Photograph taken by Patrick Coin, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=643830
Photo Six from CC BY-SA 2.5, https://en.wikipedia.org/w/index.php?curid=12702147
Photo Eight By Magnus Manske – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7398450