Tag: Calotropis procera

Invaders from Sodom

Calotropis procera (Asclepiadaceae) is an erect spreading shrub, commonly 1–2 m in height (maximum 5.5 m), that reproduces by seeds. It’s commonly known as Giant milkweed/Apple of Sodom and is native of Israel. C. procera leaves are opposite oblong-ovate to nearly orbicular, short-pointed to blunt at the apex with heart-shaped base, 7–18 cm long and 5–13 cm broad, slightly leathery, and have a fine coat of soft hairs. Flower clusters are umbelliform cymes that grow at or near the ends of twigs. Flowers are 1–1.5 cm long, fleshy and variable in color from white to pink, often spotted or tinged with purple. The fruits are 8–12 cm long, inflated, obliquely ovoid follicles that split and invert when mature to release flat, brown seeds with a tuft of white hairs at one end

Gyan Sharma, Manoj Kumar, Akhilesh S. Raghubanshi

Can an amateur give a more concise description of this tall plant that you see on roadsides across India? I would doubt it. Sharma, Kumar, and Raghubanshi’s main thrust in that paper is neither a description of the invasive plant, nor a further exploration of its origin, but a study of how it spreads. Each plant produces several thousand seeds a year, and they are carried by the wind. So one might naively expect that the plants spread uniformly around the original site of the founder population. The three authors find that they are actually carried much faster along roads, leapfrogging from one urban area to another along highways, and somewhat slower (but still faster than the wind) along secondary roads. They conclude that control of the weeds in urban areas is needed to control its spread to the rural areas where it poses a toxic threat to cattle.

I wasn’t aware of the economic damage that the Apple of Sodom (Calotropis procera) does when I took the photo above. I was more interested in my repeated observation over years that there are always these large black ants crawling over the flowers (I don’t know what species they are). In Israel two carpenter bees are the exclusive pollinators of the flower. The green cap at the center of the plant apparently exist to seal off the nectar from ants which would steal it. Which species pollinate these plants in India? The seeds of a plant may be carried in tires of vehicles, but unless the plant finds a local pollinator, it cannot become invasive.

Desert flowers

Aak (Calotropis procera), named rubber bush, is the typical dry area plant. You won’t find it deeper in the Thar desert, but the bushes were visible around rocks everywhere we went. In the Rann of Kutch they seem to be usually less than two meters high. Usually they attract ants, so I keep a watch on the small purple five-petalled flowers to see what kinds of ants I can spot. In Kutch, as the featured photo shows, I didn’t manage to get the flowers with any ants at all.

The succulent called Thor (Euphorbia caducifolia) is the commonest plant in this region. I spotted lots of birds sitting on a projecting stem of the bushes. You can see an Indian Robin in the photo on the left above. They can grow well above a man’s height, 3 meters often, taller sometimes. It flowers in late winter. If you want to see what the local insects are, keep a watch on its flowers at that time. They attract many of local insects wherever they grow.

Another succulent that is widely found in the desert is the Aak Thor (Cynanchum acidum). It has attractive tiny six-petalled white flowers (6 is not a Fibonacci number) which were budding from the ends of the stem; you can see them most of the year except in the winter months. It seems to be a climber. I saw stems trailing on the ground when there’s nothing else growing nearby.

The Rann of Kutch is full of many different kinds of grass or millets growing wild. I find myself completely unable to identify grasses. I’ll have to spend time learning more about this group. Many of them were in bloom at this time, immediately after the monsoon.

The low bushes of Kana (Commelina benghalensis) were very visible even from speeding cars, because of the attractive three-petalled blue flowers. There was a variant in purple which was also quite widespread. The flowers are large, petals can be half a centimeter in size. It seemed that a plant can either have blue or purple flowers, but they can grow quite close to each other. That makes me suspect that the colour is determined by genetics rather than soil.

Thorny nightshade (Solanum virginianum), Kateli in Hindi, is again a plant that is common in most dry areas in India. I’ve seen it deep inside the Thar Desert as well. Here you see the five-petalled flower poking out from under a different bush. Kateli is a spreading herb, and this particular plant was spread along the ground below this other bush. You can see it flowering around the year, except in the monsoon months.

Perhaps the commonest tree that I saw was the Khair (Senegalia catechu). It happened to be in flower. It is a typical mimosa, with the feathery leaves (called pinnate by botanists), flowers with wire-like petals, and thin gnarly trunks. They grew up to a man’s height, and spread out thorny branches which were exactly at the wrong height for me. if you add the Kair (Capparis decidua, bare caper), which I’ve written about earlier, I think I’ve listed the most widespread plants which I noticed in this area.

Milkweed

You can see milkweed (genus Calotropis), called aak in Hindi, in most parts of India. There are supposed to be three species which grow in India: the giant milkweed or crown flower (Calotropis gigantea) which you see in the featured photo, the milkweed (Calotropis procera) which you see in the photo below, and a species called Calotropis acia which I’m not sure that I have seen. I recognize the giant milkweed flower by its well separated and pointed petals and the fact that it is odourless. The milky sap which oozes from broken stems of aak is poisonous when ingested. That poison is used by several butterfly species, notably the one called Common Tiger (Danaus genutia). Its caterpillar gorges on these leaves, and incorporates the poison into its body. As a result, the caterpillar, and the adult which emerges from it, become poisonous. I’ve also seen ants swarming over milkweed, and wondered whether they use the chemicals in some way.

The flowers of C. procera also have the fivefold symmetry, but the petals are not as long and well-separated as that of the C. gigantea. If the bushes are fully grown, then one can tell the two species apart from the fact that the C. gigantea can grow substantially taller than a man, whereas the C. procera is about the same height as a tall person. I’ve never dug up one of them to examine the roots. Since they grow in arid climates, I would guess that their roots are deep and far-ranging. Very often several bushes grow near each other. I wonder whether their roots are in communication.

The colours of the flowers are variable, although most of the time they are on the spectrum of purples: from blue to red. When I first saw the white or greenish white flowers I wondered whether they are another species. But apparently the colour of flowers is not a species marker amongst milkweed. I cannot quite identify the bush whose photo you see above, because the buds haven’t opened up, but from the size I guess it is more likely to be C. gigantea. There’s been a lot of laboratory work separating the toxins from milkweed and examining their action separately and in combination.

Of all the uses of the milkweed, I guess the most widespread is its use in religion: as an offering to Shiva. The iconography of Shiva sometimes shows him with the white variety bound into his hair, giving a possible etymology to the name crown flower. The photo that you see above was taken near the temple of Omkareshwar on the banks of the Narmada. There was a whole line of such stalls on the walkway leading to the temple. I asked the lady in front of the basket what the spiny pods were, and she told me they were fruits of aak, also used in devotions. The seed pods of C. procera and C. gigantea are not spiny. So I wonder whether I have finally seen something of the elusive C. acia.