Chamaecrista nictitans
(sensitive partridge pea)

Chamaecrista nictitans is an annual leguminous herb which is widespread in the Neotropics as well as the southern and eastern USA. It has been introduced to a number of Asian countries and a number of island nations, and is listed as invasive or potentially invasive in Tonga (Space & Flynn, 2001), and as an invasive species of environmental concern in Samoa (Space & Flynn, 2002), Palau (Space et al., 2009), and Niue. It was first recorded as invasive in Niue in 1970 (Space et al., 2004). It does however receive a low risk assessment score for introduced species for Palau (score = 0 -- Space et al., 2009), and in general is low risk (score = 0) (PIER, 2013).

C. nictitans has characteristics that indicate invasiveness such as its ability to naturalize, its broad climate suitability (environmental versatility), a history of repeated introductions outside its native range, weedy growth, production of viable long-lived seed, self-compatibility, reproduction with short generation time, and good seed dispersal (PIER, 2013). On Niue, these characteristics may well have allowed it to colonise new areas of the island after cyclone disturbance, increasing its distribution (Space et al., 2004).

However, there is little evidence that it has a significant adverse impact in its introduced range – the literature refers to potential impacts (such as nitrogen enrichment or the outcompetition of native plants) rather than serious actual impacts.

It has several potential uses, for example to stabilize soils or fix nitrogen, or as forage – see the ‘Uses’ section for more information.

The species is listed as endangered in New Hampshire, USA, near the northern edge of its native range (New England Wild Flower Society, 2013).

C. nictitans is native to the Neotropics and the southern and eastern USA (USDA-ARS, 2013), and is now widely naturalized elsewhere in tropical and sub-tropical climates (PIER, 2013). It has been introduced to several island nations including Mauritius and Reunion (ILDIS, 2013), and several Pacific islands (e.g. PIER, 2013).

There is some discrepancy over its distribution in the Hawaiian Islands: Space et al. (2000b) state that C. nictitans is not present on Hawaii, yet several other sources (Wagner et al., 1999; USDA-NRCS, 2013; PIER, 2013; Carino & Daehler, 2002) contradict this, and list it as an introduced and invasive species. Similarly, Space et al. (2000a) state that C. nictitans is not present on Chuuk (Federated States of Micronesia), which is again contradicted by PIER (2013).

According to ILDIS (2013) it is present in a number of Asian countries and is native to some of them, but its native status there is not supported by other sources such as PIER (2013) (citing Wagner, 1999) and USDA-ARS (2013), which indicate that the Neotropics and parts of North America are its native range.

It has been planted experimentally in China (Hacker et al., 2001; Zhan et al., 2005), but is not known to be more widely present there.

There is risk of introduction between islands within the same region; for example C. nictitans is listed as a species of concern in Palau and is present on Koror and Malakal, but not present on Angaur, Kayangel, Pelelie, Ngercheu, the Rock Islands, Sonsoral State and Hatohobei State. It does however receive a risk assessment score = 0 for Palau (Space et al., 2009). There is also potential for introduction between Samoan islands: C. nictitans is present on Samoa and Upolu, but not Savai’i (Space & Flynn, 2002).

There is no information on the pathways of spread, however some productive uses such as soil stabilization, cut-and-carry forage (Hacker et al., 2001) or integrated pest management (Zhan et al., 2005) may provide reasons for the species to be spread deliberately (it is known to have been planted experimentally in China for these purposes).

There is currently no information on major regional or country variations in the habitats containing C. nictitans.

There is currently no evidence that C. nictitans negatively affects crops or other plants.

Genetics

C. nictitans has a chromosome number of 2n = 48, with evidence for some differences in chromosome size between different populations (Souza & Benko-Iseppon, 2004). There is currently no literature on hybridization between species of Chamaecrista.

Reproductive Biology

C. nictitans reproduces via seed and is both self-compatible and self-pollinating. Plants produce up to 30 inflorescences with 1-5 flowers each, and 1-12 seeds per fruit, but there is evidence of fruit abortion when resources are limited (Lee, 1989). Flowers are produced during summer months in temperate climates, so it would be logical to suggest that either temperature or rainfall cues determine flowering and fruiting times, but there is no literature examining this.

In Vermont, USA, seeds were found to germinate in spring, and plants begin flowering in mid-summer; axillary inflorescences each produce 1-5 flowers during late July and August, with individual plants producing up to 30 inflorescences. Flowers are open for one day. Fruits require several weeks to mature in late September/early October, and each contain 1-12 mature seeds (Lee, 1989). In Costa Rica, flowers bloom between August and January, and in May (Gargiullo et al., 2008)

Physiology and Phenology

There is little literature detailing survival strategies, adaptability and phenological variation of C. nictitans. However, it is known to be a weedy species which takes advantage of disturbance events for colonisation (Space et al., 2004). There is no evidence of differences in populations between native and exotic ranges. See above under ‘Reproductive Biology’ for information on the timing of flowering and fruiting.

Associations

C. nictitans produces nectar in extra-floral nectaries which act as a food source for ants, parasitoid wasps, laictid bees and jumping spiders. The most common ant associated with C. nictitans is Crematogaster lineolata Say (Ruhren, 2003). Plants with resident jumping spiders (Eris sp. and Metaphidippus sp.) - which feed on herbivores, ants, bees and other spiders - have been shown to set more seed than plants with no spiders, indicating that they are beneficial to plant fecundity (Ruhren & Handel, 1999).

Environmental requirements

There is no information on any specific environmental requirements of C. nictitans. Hacker et al. (2001) found that some accessions from Argentina and Paraguay survived the winter when planted in Fujian and Hunan provinces of southern China, but those from lower latitudes did not. A number of sources suggest that the species prefers light sandy soils and open sunny situations (C. Parker, consultant, UK, personal communication, 2014).

There is little information detailing natural enemies of C. nictitans; however Ruhren & Handel (1999) do state that Sennius cruentatus (Bruchidae) is a specialist seed predator of C. nictitans, and it has a range covering the eastern USA and Mexico, part of the native range of C. nictitans (Kingsolver, 2004).

Medicinal, pharmaceutical

• Traditional/folklore

Detection of the presence of C. nictitans could come from dedicated surveys and identification in the field.

According to Miller and Miller (2005), C. nictitans is similar to C. fasciculata (which is found in most US states where C. nictitans is found – USDA-NRCS, 2013), but C. nictitans has smaller leaves. (Note that Miller and Miller (2005) give a smaller size for the leaves of C. nictitans than that given by Gargiullo et al. (2005)).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

There is no information currently available detailing prevention and control methods for this species. As it is known to be weedy in habit, colonising disturbed ground, it is logical that monitoring such sites for colonisation and subsequent removal of plants would help prevent invasion.

Details of this species in general are lacking. There is very little literature dealing with its impact on natural systems: research should focus on any negative impact that it might have on native flora and fauna, so that mitigation of impacts can be undertaken. There is also little information on how and why the species has been transported outside its native range by humans historically.

USA: PIER (Pacific Island Ecosystems at Risk), University of Hawaii, Honolulu, http://www.hear.org/pier/index.html

25/03/2013: Original text by Isabel Jones, Consultant, UK.