Strobilanthes tonkinensis

Many sources still refer to the plant by the synonym Semnostachya menglaensis, but this name is not a validly published name as that herbarium where the type specimen is located was not specified.^[7]

The genus name Strobilanthes can be broken down into στροβιλοϛ (strobilus) meaning 'pine cone',^[12] and ανϑοϛ (anthos) meaning 'flower'.^[13] The specific epithet tonkinensis refers to the type locality of Tonkin (Northern Vietnam).^[1] The epithet nivea derives from the latin niveum meaning 'snow white',^[14] perhaps referring to the white flowers. The epithet menglaensis refers to Mengla County in China.^[6]

In Chinese it is called 糯米香 (nuò mǐ xiāng "glutinous rice fragrance"),^[7] because it smells and tastes like sticky rice.^[11] In Thai, it is called เนียมหอม^[15] (niamhom).^[16] The Vietnamese names for the plant include chuỳ hoa bắc bộ and cơm nếp.^[17][18] Chuỳ hoa refers to members of Strobilanthes as a whole,^[19] and Bắc Bộ refers to Northern Vietnam. The sarmentosus variety is called chuỳ hoa bắc bộ có lỏng.^[17] Khmu language speakers in Laos call it pl̀tàap.^[20]

The aroma evokes sticky rice, but has also been compared to pandan.^[16] Dried leaves of S. tonkinensis are used to flavor black tea and pu'er tea to impart its fragrance and sticky rice flavor.^[21] The use of the leaves in tea has a long tradition among the Dai people.^[22] It can also be used as a flavoring for jiuqu, cookies, ice cream, and dim sum.^[23] The herb can also be mixed with slaked lime for betel nut chewing or added to tobacco to make those strong flavors more palatable.^[24]

Outside of food or drink, the leaves can be used to give laundry a fresh scent.^[24]

S. tonkinensis appears related to S. maculatus, but has much larger flowers, leaves, and bracts; as well as having denser trichomes.^[1] S. spathulatibracteata also is morphologically similar.^[25]

S. tonkinensis was briefly in the Strobilanthes subgenus Sympagis.^[5] The subgenus was subsequently elevated to genus status,^[5] before being determined to be a synonym of Strobilanthes,^[26] which now has no subgenera.

The variety Strobilanthes tonkinensis var. sarmentosus is so named because it has sarmentose (long and slender) branches.^[3]

When the chloroplast genome was sequenced, it was compared to other species within Acanthaceae and the below maximum likelihood phylogenetic tree was produced.^[8] The numbers on the nodes are the bootstrap values.^[8]

The plant is herbaceous with a woody base and shrubby, roughly four-sided, pubescent branches.^[1][7] When dry the plant is fragrant.^[7]

The leaves are ~23×12 cm or a little smaller and egg-shaped, starting wide and narrowing quickly to the acuminate apex (tip). The margins are nearly entire, with irregular sinuous 'teeth'. The leaf epidermal cells are hexagonal with straight cell walls.^[27] The leaf stomata are hypostomatic (on the abaxial side) and solely diacytic.^[27] The non-glandular leaf trichomes tend to be simple, composed of two cells, and cone-shaped.^[27] The leaf petioles are 3–4 cm long.^[1] Adaxially there are prominent striated cystoliths^[1][7] with a point on one end.^[27]

S. tonkinensis has white flowers that are opposite, arising from pedunculate, tomentose spikelets in the upper axils.^[1] The flowers are in lax, terminal spikes similar to Strobilanthes collina.^[28] The bracts are 10×3 mm, slightly spathulate, obtuse, and densely tomentose.^[1] Bracteoles are 6×1 mm in size, lanceolate, obtuse, and densely tomentose.^[1] The calyx is also obtuse and tomentose, and about 8.5×1.4 mm.^[1] The corolla lobes are short and 6x6 mm with a subacute and sinuate apex.^[1] The stamen filaments are hairy and laterally bifurcated at the base with a pubescent line running down.^[1] Anthers are 3.5 mm long.^[1] The pollen grains are 85×60 μm.^[1] The stylus is 20 mm long and glabrous with a 3 mm stigma.^[1]

The capsule is 15 mm long and 4 mm wide, with a compressed base and acute apex.^[1] It's minutely glandular-pubescentand contains four glabrous seeds.^[1] The glabrous seed is unusual among Strobilanthes of East Asia.^[29] The seeds have no trichomes on their areoles, only annular thickenings.^[29]

The plant can typically be found in tropical and subtropical moist broadleaf forests at 200–1500 m in elevation in Vietnam, Thailand, China (Yunnan and Guangxi),^[7] Laos,^[30] Indonesia (Sumatra),^[27] and Myanmar (Chin State and Tanintharyi Region).^[31]

S. tonkinensis cannot grow in direct sunlight, nor in conditions that are too shaded or moist.^[16]

The type was found by Benjamin Balansa in Tonkin (Northern Vietnam) in the forests of the Ba Vì mountain range at 400 m in elevation.^[1]

Dried S. tonkinensis leaves contains abundant minerals and trace elements, particularly high levels of calcium, potassium, magnesium, and phosphorus.^[11] Additionally, it contains essential trace elements such as iron, copper, manganese, and zinc, which are necessary for human health.^[11] The plant is rich in nutrients such as crude protein, crude fiber, and amino acids, with a high content of essential amino acids that meets the Food and Agriculture Organization and World Health Organization's recommended ratio.^[11]

The volatile molecules the contribute to the aroma include α-ionone, trans-β-ionone, linalool oxide (pyranoid), isophorone, formic acid dodecyl ester, acetophenone, 6-methyl-pentadecane, 4-chloro-2-methyl-1-phenyl-3-buten-1-ol, 3-octanol, 3-hexenyl ester, 3-carene, 3,6,6-trimethyl-bicyclo(3.1.1)hept-2-ene, 2-hydroxy-benzoic acid ethyl ester, 2-ethyl-1-hexanol, 1-phenyl-1,2-propanediol, 1-octen-3-ol, 1-nonanol, 1-dodecanol, 1,7,7-trimethyl-bicyclo(2.2.1)hept-2-ene, and (Z)-butanoic acid.^[21]

S. tonkinensis flowers from April–June and in December, and fruits in June and July.^[7]