Comprehensive Description

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Costus laevis (Costaceae) is an understory shrub that is found in the New World Tropics, from Guatemala to Bolivia at altidudes of 0-900 m (Gargiullo et al. 2008). It is found in lowland wet forests and prefers light gaps along streams, roads, and in forests. They require light gaps for germination and establishment but they can continue to fruit and flower if the forest regenerates and they become shaded (Schemske 1983a). The leaf arrangement of C. laevis is simple, alternate in a spiral growth with the leaves being long, pointed and about 15-60 cm long and 5-15 cm in width (Gargiullo et al. 2008). Petioles are sheathed, giving leaves a sessile appearance. The plant can grow up to 1-6 m tall with the youngest growth being red (Gargiullo et al. 2008). The flowers of C. laevis are asymmetrical and white with yellow center and have a large projecting labellum that is dark red with pale yellow stripes and they tend to be 5-9 cm long (Gargiullo et al. 2008, Schemske 1982). Flowers are formed on a pinecone inflorescence that is composed of broad overlapping green bracts that cover the immature flowers (Schemske 1983b). They flower one or two at a time and open at dawn and fall in the afternoon (Schemske 1983b). C. laevis can flower all year, but peak flowering is from May to August, which is the early to middle of the rainy season (Schemske 1983b). The primary pollinators are female euglossine bees, being responsible for 95% of the pollination (Schemske 1983b). Hummingbirds or self-compatibility do the other 5% but this is extremely rare (Schemske 1983b). The fruits of C. laevis are black seeds covered in a waxy white aril that are 2-3mm long (Schemske 1983b). The plant fruits from September to October when the bract opens to reveal the fruits. The white fruit contrast with the bright red of the inner bract. This display attracts birds that eat the white aril and disperse the seeds (Schemske 1983a). A common predator is the blue-black grosbeak, which is an understory finch that eats mature or immature fruits by opening the bracts and eating the seeds (Schemske 1983b). Another predator is Cholus cinctus (a black and yellow weevil) that drills into the bracts destroying the new flower buds and the inflorescence in general. Mostly the weevils just decrease the amount of flower production by destroying part some of the bracts (Schemske 1983b). To decrease the amount of predators on the plant, C. laevis has extrafloral nectaries that attract as many as 24 species of ants to protect the plant and decrease the amount of predation. Bracts near mature flowers have active nectar sites. The plant may have evolved a specific morphology and chemical characteristics to increase its chances of having an ant species visit it with the best defense mechanisms (Schemske 1982). Monacis bispinosus and Ectatomma tuberculatum ants mostly protect Costus laevis according to a study by Schemske but they do not give protection against weevils. Only when Azteca ants were present on C. laevis is it free from predators (Schemske 1983b).


Creative Commons Attribution 3.0 (CC BY 3.0)

© Brendon Donoghue, Alyssa Biagini

Source: CIEE Tropical Ecology and Conservation Program

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