Holmskioldia sanguinea (Chinese hat plant)

H. sanguinea is a climbing shrub currently considered a low risk species according to a risk assessment prepared by PIER (2014) and is not yet known to be invasive (Gilman, 1999). The species is woody and persistent, reproduces by cuttings, air layering, or seeds which are viable and can survive passage through the gut, and can tolerate a wide range of soil conditions (Gilman, 1999; Whistler, 2000; Govaerts, 2014; PIER, 2014). However it is unlikely to spread as a contaminant of produce or soil, and its seeds are not adapted for wind dispersal and do not have thorns or burs to increase movement by hitchhiking (PIER, 2014). Monitoring, prevention and control of H. sanguinea is unnecessary at this time, but the species may pose a threat in the future as it continues to be intentionally spread for use as an ornamental.

The Lamiaceae, or mint family, is a family of herbs, shrubs, and trees comprising about 200 genera and 3,200 species, many with a long history of medicinal and food use, and characterized by their aromatic herbage, quadrangular stems, and verticillate inflorescences (University of Hawaii, 2014). This family includes some of the most well-known herbs including lavender, sage, basil, mint and oregano.

Holmskioldia currently includes only one accepted species, H. sanguinea (The Plant List, 2013). The genus is named for Danish scientist Theodor Holmskiold (Holm; Holmskjold) (1732-1794), a nobleman, botanist and physician (Stearn, 1992; Quattrocchi, 2012). H. sanguinea is an often cultivated ornamental plant and is named for its red, showy flowers. Its common names, Chinese hat plant and cup-and-saucer plant, are due to the shape of its flowers, a saucer-shaped calyx under a two-lipped funnel-shaped corolla.

Several species previously included in the genus Holmskioldia have been transferred to Karomia, a genus first described in 1932.

Scandent or erect shrub, with numerous basal branches, attaining 2 m in length. Stems obtusely quadrangular or cylindrical, puberulent, grayish; stipules absent. Leaves opposite, 3-12 × 1.5-8.5 cm, ovate or ovate-lanceolate, chartaceous, the apex acuminate or acute, the base cuneate or truncate, the margins serrate; upper surface puberulent, dark green, dull; lower surface puberulent, pale green, with numerous dots, the venation prominent; petioles 8-30 mm long, puberulent. Inflorescences of racemes or less frequently panicles, axillary or terminal, up to 5cm long; bracts minute; pedicels 2.5-8 mm long, slender, glandular-pubescent. Calyx acetabuliform, orange, 1.6-2.2 cm in diameter, with minute dots; corolla hypocrateriform, crimson, 1.5-2.5 cm long; stamens slightly exserted, the filaments pink; ovary glabrous, the style as long as the filaments. Fruit globose, brown, verrucose. [Acevedo-Rodriguez, 2005].

H. sanguinea is native to the Eastern and Western Himalayan regions including Nepal, Myanmar, Bhutan, Bangladesh and India, and has been distributed around the world as an ornamental, with records of its cultivation in the Americas, Europe, Indo-China, Asia-Pacific, and southern Africa (Whistler, 2000; Glen, 2002; Govaerts, 2014; PIER, 2014; USDA-ARS, 2014). The species has been introduced to the West Indies including the Leeward and Windward Islands (Govaerts, 2014). 

H. sanguinea is native to the Eastern and Western Himalayan regions but has been widely cultivated and naturalized throughout southern Asia, Mauritius, Indonesia and the West Indies (Whistler, 2000; PIER, 2014). The species was apparently imported to the UK around 1796 from China by way of Calcutta (Botanical Register, 1823; Jacques, 1833). In 1804 it was being promoted as an exotic, new, rare, and cultivation-worthy plant in Britain (Smith, 1804); in 1823 the Botanical Register credited the species’ introduction to the UK to Peter Good, and cited Retzius that the species was brought originally from China into the Botanic Garden at Calcutta, though it was “native of the interior parts of Bengal” (Botanical Register, 1823). Despite the early date of introduction to England, the species was not introduced to Parisian botanical gardens until years later (Jacques, 1833).

Date of the species’ introduction to the West Indies is uncertain. It may have occurred much later than its introduction to Europe, sometime in the early 1900s. Specimens were collected in Jamaica and Haiti in the 1920s (US Herbarium collections), but the species does not seem to be a well-known plant from this region and was not included in some major works around this time including Bello’s work on Puerto Rico (1881; 1883), Urban’s flora on the Antilles (Urban, 1898-1928), and Britton and Millspaugh’s work on the Bahamas (1920). Today the species is widely known as a cultivated garden plant or curiosity. 

Risk of introduction for this species is currently low. In a risk assessment prepared for Hawaii, H. sanguinea received a low score of -1 (score greater than 6 = reject for import; likely to be major pest) (PIER, 2014). The species is woody and persistent and possesses several invasive traits, including its intentional and repeated introduction outside of its native range, propagation by cuttings, air layering, or seeds which are viable and can survive passage through the gut, and tolerance of a wide range of soil conditions (Gilman, 1999; Whistler, 2000; Govaerts, 2014; PIER, 2014). However, the species has a minimum regenerative time of 3 years, requires specialist pollinators, and is unlikely to spread as a contaminant of produce or soil. Its seeds are not adapted for wind dispersal and do not have thorns or burs to increase movement by hitchhiking (PIER, 2014). Considering these factors, although H. sanguinea is not known to be invasive (Gilman, 1999) and is not considered a high risk species, the species could pose a threat in the future.

The seeds of this species have no means of attachment and are unlikely to be dispersed externally by animals, but they are encased in berries and can survive passage through the gut, as they are known to be dispersed by birds (PIER, 2014). Seeds are not adapted for wind dispersal.

H. sanguinea has been transported beyond its native range for use as an ornamental, and in the USA is used as a border and hedge plant (Gilman, 1999; USDA-ARS, 2014). H. sanguinea can regenerate by cuttings, trimmings and in garden waste which might result in the species’ escape from cultivation.

H. sanguinea is a popular ornamental and is native to subtropical, submontane habitats (USDA-ARS, 2014). It occurs in the sub-Himalayan tracts of India, Nepal, Bhutan, Sikkim, and Bangladesh (Flora of Pakistan, 2014). In the Himalayas, from Kumaun to Bhutan, the species has reportedly grown at elevations between 300-1500 m (Nepal Checklist, 2014). In Bolivia the species is found in lowlands, 0-500 m, and has been reported in rainforests (Bolivia Checklist, 2014). In Panama the species has been observed between 0-1000 m (Panama Checklist, 2014) and in Antioquia, Colombia the species occurs in submontane humid forests (Vascular Plants of Antioquia, 2014). It has also been reported growing in coastal areas in Ecuador (Vascular Plants of Ecuador, 2014).

Although H. sanguinea poses a low risk of introduction and is not known to be invasive, it is grown as an ornamental and used as a hedge and border plant in cultivated areas. Its invasive characteristics, which include its woodiness and persistence, tolerance of various soil conditions, and ability to reproduce by cuttings, could cause minor disruption to agriculture or unwanted growth within home gardens (Gilman, 1999; Govaerts, 2014; PIER, 2014). The species could possibly be a fire hazard if allowed to grow unpruned, as it can accumulate dry canes (PIER, 2014).

H. sanguinea is cultivated as an ornamental and used as a border and hedge plant (Gilman, 1999; USDA-ARS, 2014). It is also reportedly used in traditional medicine. Crushed fresh leaves and shoots are applied in rheumatism and rheumatoid arthritis; extracts of leaves and stembark are taken for dysentery, headaches, and high blood pressure, while leaves are boiled as part of a blood purifying concoction. Leaves and flowers are also believed to have magico-ritual significance, especially in treating children’s diseases (Quattrocchi, 2012).

H. sanguinea is not considered a high-risk or potential invasive species, but increased cultivation and introduction as a hedge plant could allow for accidental escape. Considering its lack of widespread popularity as an ornamental, however, monitoring of this particular species is not necessary at this time. A re-evaluation of the species’ distribution and risk is recommended in the future.