Premna microphylla

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 a tree^[4] and has square, woody, mostly smooth stems and branches.^[2] The plant reaches 2–6 m (6 ft 7 in – 19 ft 8 in) in height,^[10] and around 3 m (9.8 ft) wide.^[6] It grows as 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 of Serissa.^[14]

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.^[15]

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.^[16]

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.^[17] 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%).^[18][19] 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 burn specific wood for the ash, such as Osmanthus.^[20] 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%).^[21]

The plant is also used for bonsai^[6] because of its small, strong-smelling leaves.^[14] The bonsai trunks are evocative of driftwood, similar to shimpaku juniper.^[14] A specimen of P. microphylla was used as an autonomous bonsai in the art installation titled Premna Daemon.^{[22][23][24][25]}