Premna microphylla
Premna microphylla
Conservation status
Least Concern  ( IUCN 3.1) [1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Lamiales
Family:	Lamiaceae
Genus:	Premna
Species:	P. microphylla
Binomial name
Premna microphylla Turcz. 1863 [2]
Synonyms [3]
Gumira japonica ( Miq.) Kuntze Gumira microphylla ( Turcz.) Kuntze ( homotypic synonym) Premna formosana Maxim. Premna japonica Miq. Premna luxurians Nakai Premna microphylla var. glabra Nakai Premna microphylla var. luxurians ( Nakai) Moldenke

Premna microphylla is a tree ^[4] in the mint family ( Lamiaceae). ^[3]

P. microphylla has the English common names Japanese premna, ^[5] (Japanese) musk maple, ^[6] and Japanese neem tree. ^[6] It is also called tofu tree because of the tofu-like food made from the leaves. ^[7]

The specific epithet microphylla derives from Greek μικροϛ (micros) and φυλλον (phyllon) and means 'small leaves'. ^{[6] [8]} The name for the genus Premna derives from the Greek πρέμνον (premnon, tree stump) refers to the short trunks that some species have. ^[6]

In Japanese it is called ハマクサギ (hamakusagi). ^[4] In China, it is known as 豆腐柴 (dòufu chái 'tofu wood'), 斑鸠树 (bānjiū shù ' turtledove tree'), ^[9] 臭黄荆 (chòu huáng jīng 'stinky yellow thorn'), 腐蜱 (fǔ pí 'rotten tick'), and 观音草 (guānyīn cǎo ' Guanyin grass'). ^[10] In Taiwan it is called 臭黃荊 (chòu huáng jīng) ^[11] The plant is called cách lá nhỏ in Vietnamese. ^{[12] [13]}

P. microphylla is used for food. The leaves can be used to make a pectin-rich gel that is something like tofu. ^{[10] [9]} The jelly is similar to grass jelly but it not usually called that, unlike other grass jelly plants. This green gel is called 神仙豆腐 (shénxiān dòufu, immortal/divine tofu) ^[9] or 观音豆腐 (Guānyīn dòufu, Guanyin tofu). ^[10] In English it is sometimes called green leaf tofu. ^[7] A similar 'fairy tofu' is made from the leaves of Premna puberula. ^[14] The leaves are high in protein (13.48%), ^[10] and while not as much as soybeans, it is high for a leaf vegetable and ranks closer to cereal grains like hard wheat (12.6%) rather than spinach (2.9%). ^{[15] [16]} To make the 'tofu', the leaves are washed and crushed with some water to facilitate grinding. ^[10] Culinary ash is added to the strained mixture and it is allowed to set. ^[10] Some cooks use burn specific wood for the ash, such as Osmanthus. ^[17] The dish is considered a refreshing summer treat. ^[10] Production is small and local, and not done on an industrial scale. ^[10]

Much effort has been made to develop P. microphylla as an industrial source of pectin. ^[10] The leaves contain 30-40% pectin, ^[10] much higher than the typical sources, apple pomace (10-15%) and citrus peel (20-30%). ^[18]

The plant is also used for bonsai ^[6] because of its small, strong-smelling leaves. ^[19] The bonsai trunks are evocative of driftwood, similar to shimpaku juniper. ^[19] A specimen of P. microphylla was used as an autonomous bonsai in the art installation titled Premna Daemon. ^{[20] [21] [22] [23]}

P. microphylla is a tree ^[4] and has square, woody, mostly smooth stems and branches. ^[2] The plant reaches 2–6 m in height, ^[10] and ~3 m wide. ^[6] It grows and a nanophanerophyte or phanerophyte. ^[3]

The leaves are sessile, ovate- lanceolate in shape and tapered near the tip. ^[2] The leaves grow in an opposite pattern. ^[6] The leaf margins are serrate from the middle to the apex. ^[2] Both sides of the leaves are scabrous and covered with very short 'hairs'. ^[2] The leaves have a strong odor ^[10] that has been compared to those Serissa. ^[19]

The flowers are hermaphroditic ^[2] and grow in conical panicles. ^[6] The 5-part calyx is short, ^[2] cup-shaped, and purplish-green. ^[6] The calyx surrounds a funnel-shaped corolla ^[2] that is pale yellow. ^{[10] [6]} The petals are 0.3–0.4 inches (7.6–10.2 mm) long. ^[2] The cream-colored and zygomorphic flowers bloom in May and August ^[4]

The drupe is obovate to nearly spherical and purple-black when ripe. ^{[10] [6]}

Major compounds found in the essential oil include blumenol c, β-cedrene, limonene, α-guaiene, cryptone, and α-cyperone. ^[24]

The plant is found in southern China, ^{[2] [3] [6]} central and southern Japan, ^{[3] [4]} and Taiwan. ^{[3] [11] [6]} The type specimen was collected by Scottish botanist and plant hunter Robert Fortune in China. ^[2] It prefers growing in slightly acidic to acidic soil mainly on woodland edges or understory at an altitude of 500–1,000 metres (1,600–3,300 ft) in elevation. ^[10]

The growing season is yearly from March to November. ^[10] The pollination syndrome for P. microphylla is melittophily, with bee and wasp pollinators including Xylocopa amamensis, Cerceris yuwanensis, and Hylaeus insularum. ^[4] There are no major diseases or insect pests known. ^[6] There is some evidence that sika deer will nibble on the tree occasionally. ^[25]