letting nature back in

An African tree renowned for its beauty is the Cape chestnut, which is a larval host plant of the citrus swallowtail butterfly that featured in last week’s post. We are fortunate to have one of these trees at the bottom of the garden and it is mature enough to flower each summer.

Citrus swallowtail butterflies lay their eggs on larval host plants that occur in only two families of plants. Like many other species of swallowtail butterflies in the Papilionidae family, their larval host plants are in the Rutaceae (citrus) and Apiaciae (carrot) families.

In addition to our small potted cooking leaf lime (Citrus hystrix), we have several plants in our garden that also host citrus swallowtail larvae (caterpillars). The Cape chestnut (Calodendrum capense) is the largest and the most impressive.

The Cape chestnut tree that grows at the bottom of our garden in flower with the leaves still spotted with raindrops after summer rain

The tree that grows just outside our fence line was planted by the previous occupants of our house. It is currently over 12 metres (about 30 feet) in height and is in the region of 20 years old. The Cape chestnut is known to be a late developer – when grown from seed it rarely flowers before it is about 8 years old.

Typically the Cape chestnut has a high rounded crown, and I had to zoom in to get a close-up of the flowers that are high up in the tree at the bottom of our garden

The other common name for this tree is wild chestnut. It was named as a chestnut by William Burchell (1782-1863) because of similarities in flower and fruit to the horse chestnut that he was familiar with, although these trees are not related. Burchell was an English explorer, naturalist, artist and writer who’s travels included an expedition in South Africa when he collected over 50,000 mostly botanical specimens.

The botanical name Calodendrum capense means beautiful (kalos) tree (dendron) from the Cape (capense). Indeed it is a beautiful tree, and although it was named in the Cape by botanist Carl Peter Thunberg (1743-1828), it is not limited to the Cape and occurs across southern Africa and into tropical Africa as far north as Ethiopia.

The Cape/wild chestnut is a tree of the forest. This photograph of Cape chestnut trees in flower was taken as the morning mist was dissipating in a patch of mistbelt forest next to farmland in the KwaZulu-Natal Midlands

 The Cape chestnut is evergreen at the coast where conditions tend to be warmer all year round, and it is semi-deciduous to deciduous inland. The tree outside our garden sheds its leaves at the end of winter and the leaves start budding in the early spring. The leaves, typical of all Rutaceae (citrus) species, are dotted with oil glands. Consequently the leaves are aromatic when crushed exuding a soft almost lemony smell.

A mature Cape chestnut in full flower is a sight to see. This photograph was taken in the KwaZulu-Natal (KZN) Midlands

The Cape chestnut is known for its pink flowers, but some trees have white flowers. We came across only one tree with white flowers in a patch of mistbelt forest in the KZN Midlands

Looked at more closely, even the seemingly white flowers have pink centres

 With a non-invasive root system and its attractive flowers, the Cape chestnut is used as a street tree and is popular in larger gardens. I gather it is sought after as an ornamental tree in other continents too, including Australia.

Its pale yellow hard wood is easily worked and has many uses, past and present, including tent bows, wagon-making, yokes, planking, shovel handles and furniture, and in the past at least was considered one of the most generally useful hard woods. It can also be used for firewood and to make charcoal. 

The flowers attract insects including bees and butterflies, but apparently they do not attract birds

A green seed capsule of a Cape chestnut found on the floor of mistbelt forest in KZN

The seed capsule is woody and as it ripens it splits into five lobes and eventually spills its black seeds. The seeds are eaten by samango and vervet monkeys and also by African olive (formerly rameron) pigeons, lemon (formerly cinnamon) doves and by Cape parrots. When the black seed coverings are opened the kernels within are like pale nuts.

Lying on the forest floor, a ripe seed capsule that has split to reveal the black seeds within 

The kernels can be crushed and boiled to make an oil that can be used to make soap. The oil is also used as a skin moisturiser known as yangu oil. The bark too is used as an ingredient for facial skin care.

A seed capsule that I left outside (we were planning to plant the seeds), which was found and torn open by a vervet monkey. Fragments of kernel left by the monkey can be seen to the left of the two black seeds that have been released from the capsule. Vervet and samango monkeys play an important role as seed dispersers of many trees and other plants 

Although the Cape chestnut is a larval host plant of the citrus swallowtail (Papilio demodocus) butterfly, I have not noticed the butterflies seeking out this tree in particular. What I did do though, was check up on the immature instar caterpillar on our potted lime tree. During the past week the caterpillar has moulted and in the process changed from black and white to the green colours of the mature caterpillar.

The citrus swallowtail caterpillar still in its early form last week

The same caterpillar in its next form (instar) two days later 

The citrus swallowtail caterpillars take about 4 weeks to develop passing through 4 or 5 instars in the process. The mature caterpillar is around 45 mm (1.7 inches) in length. After shedding its skin (cuticle) it eats the shed cuticle, presumably for its nutritional value, before resuming leaf eating. The new cuticle has folds to allow for a degree of expansion as the caterpillar grows larger.

Despite its size the caterpillar is well camouflaged against the green leaves and can be quite difficult to see even when one has a general idea where it is. Today when I went out to look for it, I couldn’t find it. But yesterday I photographed it in the company of a grasshopper.

The grasshopper stretching its legs with the caterpillar visible in the background

The focus is switched onto the caterpillar, which is noticeably larger than it was only a few days before. The grasshopper is just visible out of focus in the foreground 

Well, I have just been out again to look for the caterpillar, which I last saw last evening and I can’t spot it. I found a small grasshopper and a tiny jumping spider eating a fly but the caterpillar seems to be well hid. It is likely too soon for it to have pupated, and unless something unfortunate happened, I think it is concealed in a tangle of lime tree, cherry tomatoes and pepperdew plants. I hope so anyway.

Sources:

Fern, Ken. 2014. Calodendrum capense. Tropical Plants Database. http://tropical.theferns.info/viewtropical.php?id=Calodendrum+capense; Mackean, D G & Mackean Ian. 2004-2020. Papilio demodocus – the Citrus Swallowtail Butterfly. Resources for Biology Teaching by D G Mackean. http://www.biology-resources.com/insect-papilio-01.html; Notten, Alice. 2001. Calodendrum capense. South African National Biodiversity Institute (SANBI). PlantZAfrica.com http://pza.sanbi.org/calodendrum-capense; Robertson, Hamish. [n.d.] Papilio demodocus (Citrus swallowtail). Biodiversity Explorer. http://www.biodiversityexplorer.info/butterflies/papilionidae/papilio_demodocus.htm

Posted by Carol