A cheerful plant to grow – Crotalaria retusa

Known via a range of common names which include devil bean, large yellow rattlebox and wedge-leaved crotalaria, Crotalaria retusa is a highly ornamental plant that you can grow in your garden. A member of the bean family (Fabaceae), it produces bright yellow flowers that are borne on an upright spike which is presented promindantly above a mass of jade green leaves. For ornamental purposes, this plant is best grown in mass in either a flowerbed or as a border plant.

Sometimes found growing as a weed in wastelands, Crotalaria retusa grows as an annual herbaceous shrub that can attain a height of about 1 m. This plant can only be from seeds and the process is an easy one but trying to get some seeds can prove to be difficult. It loves a sunny spot that is also well draining. Being a legume, Crotalaria retusa can fix its own nitrogen from the atmosphere and hence can be grown in nitrogen-poor soils.

Besides being useful as an ornamental plant, Crotalaria retusa has an interesting characteristic that will probably interest kids. The pod-like fruit this plant produces, when mature and dry, becomes a rattlebox that can be shaken and heard. The common name of this plant ‘rattlebox’ is derived from this interesting feature.  The genus name Crotalaria is derived from the Greek word, κροταλον, which refers to the musical percussion instrument castanet. If you are looking for a candidate to grow in your sensory garden, plant Crotalaria retusa in it to confer the sound/audible component.

Like other legumes, Crotalaria retusa can be grown as a green manure, where mature plants can be worked back into the soil to add nitrogen. It is also grown as a source of plant-derived fibre and dye.  Crotalaria retusa is also grown as a medicinal plant. According to Plant Resources of South East Asia (PROSEA), its roots are used against coughing up blood while its leaves are mixed with those of another relative, Crotalaria quinquefolia, and consumed or applied externally against fever, scabies, lung diseases and impetigo. Flowers and leaves are both edible as vegetables due to their low alkaloid content and are purportedly sweet. Seeds are roasted and eaten in Vietnam. Note that this plant is also nematode-resistant and studies have found dried plant parts can be worked into the soil as a soil amendments to deter and reduce root galling by the root-knot nematode, Meloidogyne incognita.

Lastly, note that Crotalaria retusa is a butterfly host plant. According to the Butterfly Circle website, Crotalaria retusa is the food plant for the pea blue butterfly (Lampides boeticus). Unlike other butterfly caterpillars that chew up leaves, the first two instars of the pea blue bore into flower buds of this plant and consume the flower parts contained within. The larger 3rd and final instar caterpillars will move on to eat the developing seeds within seed pods. For more information on the pea blue butterfly, please refer to the webpage below:

http://butterflycircle.blogspot.com/2009_09_12_archive.html

Do your part for the wildlife and environment around us, try to grow this plant without the use of pesticides. In rapidly urbanising Singapore, we are losing loads of our native species of flora and fauna without many of us knowing. Butterflies have an important role in our environment and one of the most obvious role they play is that of a pollinator where they help to transfer pollen that help plants to set seed and ensure the survival of subsequent generations.

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3 responses to “A cheerful plant to grow – Crotalaria retusa

  1. Crotalaria spp. – Rattlebox or rattlepod is reportedly toxic to equines. Is this the same plant?

  2. I believe several of the crotalaria species are responsible for the death of equines.

    I have taken one from the hills of lake toba, with smaller flowers. It seems to do poorly here in Singapore. It was flowering very well in cleared land at an altitude of 3000 feet.

    I also managed to get my hands on Crotalaria cunninghamii. Managed to germinate it after following some web instructions on treating the seeds with hot water.

    Hopefully I get them to flower. The C. cunninghamii is the green bird flower and has blossoms that look like humming birds.

    Wilson,

    I am trying to propagate the C. ratusa by cuttings. We are trying to mass produce them in our resort in Lake Toba. It is easy to maintain and gives a very dramatic effect when they flower. I noticed that this plant has a hollow core in its stems. Maybe at the end of the day it is just easier to propagate from seeds as they are really abundant.

    The carpenter bee visits the plant every day at about the same time in the evening.

    Still waiting to see what kind of moth/butterfly will use it as host here in Singapore.

    In Lake Toba, the native crotalaria plants are infested with caterpillars of moths. The end up eventually in the seed pods.

  3. I just confirmed that these really do no grow from cuttings. The stems are quite thin from the actively growing regions. The centre of the stem is hollow and rot very quickly when planted in moist soil.

    Will try a thicker stem next time.

    But seriously, with so much seed production and ease of germination, I think I really should not bother about stem cuttings.

    Hot water soaking seems to help germination too.

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