Blackboard Tree: Classification, Distribution, Characteristics, and Uses

Introduction

Alstonia scholar, referred to as the Devil Tree or Blackboard Tree is an evergreen tree with a height of up to 100 metres. It is used to treat ulcers, dropsy, chronic diarrhoea, dysentery, bowel motions, beriberi, and liver congestion. An indigenous evergreen tropical tree to the Indian subcontinent and Southeast Asia, Alstonia scholaris has a milky sap that contains a deadly alkaloid and a rough, greyish bark.

 The plant is huge, reaching heights of 17 to 20 m, with a straight, frequently grooved, and supported bole that measures around 110 cm in diameter. The bitter-tasting, tough, lenticellate-rich, and grayish-brown bark secretes white, milky latex. Coriaceous, elliptic-oblong leaves that are 4–7 in a whorl. Small, greenish-white, numerous in umbellate panicles, with a short, intensely perfumed corolla tube, are the flowers. Follicles in fruits can be 30 to 60 cm long. Papillose seeds have brownish hairs on each end. The bark, also known as dita bark, has long been used as a source of treatment for bacterial infections, malarial fever, toothaches, rheumatism, snakebite, diarrhoea, bowel disorders, etc. by various ethnic groups in Northeast India and other areas of the world. In addition, latex is used to treat fever, wounds, and coughing. It has lovely foliage and a substantial canopy, and as a result, it is a tree that is frequently used as an ornamental tree in gardens and landscapes in the warm and temperate regions of Florida, Texas, and California in the United States.

Classification

 Kingdom: Plantae

Order: Gentianales

Family: Apocynaceae

Genus: Alstonia

Species: Alstonia scholaris

Common Name: Blackboard Tree,  Milkwood Tree, Scholar Tree,  and Devil’s tree 

Distribution

Native to Southeast Asia, Africa, Northern Australia, the Solomon Islands, Pakistan, Nepal, India, Sri Lanka, Thailand, Burma, Malaysia, and Southern China.

The plant is grown in lowland and mountain rainforests in Queensland, Southern China, India, and the Asia-Pacific (Wiart, 2006). The plant can be found in all of India’s humid regions, although it is particularly common in West Bengal and the south Indian west coast forests. The species can be found in the sub-Himalayan region east of the Yamuna River and at elevations of up to 1000 m. It grows naturally in moist, subtropical, and tropical deciduous woods in India and is extensively cultivated there as an avenue tree.

Habitat

A dominating canopy species that grows in palm-dominated forests, coastal mesophyll vine forests, and notophyll vine forests, with a canopy height of 35 to 42 metres.

Characteristics

1. Saptaparna is a medium-sized evergreen tree with a typical height of 12 to 18 metres and a maximum height of 27 metres.

2. Its bark is tough, whitish to greyish white within, and when cut, it exudes a bitter yellowish latex.

3. The leaves are four to seven in number, thick, oblong, and have a blunt tip. On top, they are a dark green colour, while on the dorsal side, they are light and coated in brownish pubescence. The petioles are 6–12 mm long, the leaves are thick, dark green, grouped in whorls, obovate to oblanceolate, narrow at the base, whole, rounded, or bluntly acuminate at the apex.

4. Young branches lenticellate, branches whorled, and bark that is internally tough and yellow-gray; when the bark is damaged, milky fluid leaks out.

5. Small, umbellate-branched flowers that are greenish white. They are 7 to 10 mm in length, have a hairy tube, lobes that are 1.5 to 4 mm long, overlapping on the left, and potent perfume. India’s flowering season is from December to March.

6. The fruits are two follicles that are narrowly winged on one suture, linear, 20–50 cm long, and glabrous. The fruiting season in India is from May through July.

7. The seeds are brownish hairy tufts that are oblong, flattened, and 6 to 8 mm long.

Climate and soil

In India, the plant can be grown in a range of climates, from dry tropical to sub-temperate. However, because it prefers a very moist habitat, it does well when there is an annual rainfall of between 100 and 150 cm. The species thrives in red alluvial soil with adequate aeration. It can also flourish on black cotton soils, however, because of the generally damp soil conditions during the rainy season, growth is slow.

Propagation and cultivation

The tree may occasionally be placed in gardens for decorative purposes. It grows quickly from seeds and prefers moderate moisture levels. Altitude required: 0-900 M The average annual rainfall is between 1200 and 1400 mm, and the soil type includes alluvial, basaltic red, yellow, and sandy grey soil.

Phytochemistry

Alkaloids, coumarins, flavonoids, leucoanthocyanins, reducing sugars, simple phenolics, steroids, saponins, and tannins are all frequently found in the A. scholaris plant. Eight elements, including Cu, Zn, Fe, Ca, Cr, Mn, and Cd, are present in the leaf extract. Four picrin type monoterpenoids—5-methoxyaspidophylline, picrinine, picralinal, and 5-methoxystrictamine—are present in the ethanolic extract of leaves. The first seco-uleine alkaloids are present in the methanolic extract of leaves. Alstonic acids A and B, 2, 3-secofernane triterpenoids, and the indole alkaloid N-methyl-picrine are all present in the hydroalcoholic extract of the leaves.

Uses

In India, various portions of A. scholaris have been utilised in ayurvedic, siddha, and Unani medicine to treat conditions like cancer, malaria, gastrointestinal disorders, and jaundice. The bark of A. scholaris is used as a laxative, antipyretic, astringent, cardiotonic, and to treat skin conditions such as bronchitis, ulcers, leprosy, and pruritis. Historically, leaves have been used to treat conditions like dysentery, diarrhoea, and malaria. Fruits are used to treat epilepsy as well as tonics and anthelmintics.

Bark

The bark of A. scholaris is beneficial for skin conditions, dyspepsia, stomach ailments, and malarial fevers. The bark has laxative, anthelmintic, antipyretic, stomachic, cardiotonic, and tonic properties. It is also bitter and astringent. According to reports, the bark extract has hepatoprotective, antiplasmodial, immunostimulant, and anticancer effects. According to Ayurveda, soaking the plant’s bark in water overnight can lower blood glucose levels following oral ingestion. Additionally, bark has galactagogue, febrifuge, and depurative properties. Leprosy, skin conditions, pruritis, chronic and nasty ulcers, asthma, bronchitis, agalactia, and debility are all conditions where it works well. The milky juice is administered to wounds, ulcers, and rheumatic pains in traditional medicine; when combined with oil and poured into the ear, it soothes earaches.

Leaves

Traditional folk treatments have employed the leaves to treat a variety of ailments, including snake bites, malaria, diarrhoea, and dysentery. In some circumstances, the leaf juice functions as a potent galactagog. Beriberi, dropsy, and engorged liver treated with leaves. applied latex to tumours, wounds, ulcers, and rheumatic swellings.

Fruits

The plant’s mature fruits are used to treat epilepsy and syphilis. As a tonic, antiperiodic, and anthelmintic, it is also employed.

Pharmacological Activities

Antibacterial activity

Gram-positive bacteria like Bacillus coagulans and gram-negative bacteria like Escherichia coli were shown to be sensitive to a methanolic extract of the A. scholaris bark.

Analgesic and anti-inflamatory activity

Based on multiple in vivo experiments, alkaloids found in the leaf of A. scholaris, including picrinine, vallesamine, and scholaricine, are said to have analgesic and anti-inflammatory properties. In vitro experiments showed that the alkaloids suppressed COX-1, COX-2, and 5-LOX mediators of inflammation.

Anti-arthritic and antioxidant activity

 A. scholaris ethanolic extract considerably reduced gastric lesion indices and gastric juice secretion as well as the arthritis, which was observable with arthritis index, body weight, and leukocyte infiltration. Antioxidant enzymes like glutathione, glutathione peroxidase, and superoxide dismutase were discovered to have significantly increased levels, while levels of lipid peroxidation and myeloperoxide in the articular tissue had significantly decreased.

Antitubercular activity

It has been demonstrated that methanolic extracts of A. scholaris’s leaf, stem bark, and root bark exhibit antitubercular properties. The anti-mycobacterial activity demonstrated the ability of A. scholaris extract to treat tuberculosis.

Antifertility activity

A.scholaris benzene extract contains lupeol acetate, which has been shown to have an antifertility effect.

Hepatoprotective activity

Hepatocyte function was improved by the methanolic stem bark extract of A. scholaris, and biochemical indices like SGOT, SGPT, ALP, TP, and TB were shown to be greatly reduced.

Ameliorating effect

When compared to viper venom, an aqueous bark extract of A. scholaris has been shown to lessen liver and kidney damage, which may be due to the complexation of polyphenols with venom enzymes.

Anti-cancer properties

The sulforhodamine B assay was used to test the cytotoxic activity of methanol extracts of the root barks of A. macrophylla, A. glaucescens, and A. scholaris that were collected in Thailand against the human lung cancer cell lines MOR-P (adenocarcinoma) and COR-L23 (large cell carcinoma). Villalstonine was significantly more active than pleiocarpamine, O-methyl macralstonine, and macralstonine.

Antidiabetic potential

Researchers conducted several in vitro and in vivo experiments to assess the conventional and local antidiabetic claims of A. scholaris. The -glucosidase inhibitory and hypoglycemic properties of A. scholaris were investigated about its antidiabetic potential. The leaves and stem bark of A. scholaris have been reported to possess strong anti-diabetic properties. Patients with non-insulin-dependent diabetes mellitus are consistently hypoglycemic after ingesting A. scholaris leaf powder. A. scholaris leaves powder’s hypoglycemic effects in individuals with non-insulin-dependent diabetes mellitus were attributed to their direct insulin-like and insulin-triggering effects.

Anti-diarrheal properties

The aqueous and alcoholic bark extracts of A. scholaris had antidiarrheal effects on mice, according to Patil et al.

Antimicrobial activity

The antibacterial properties of the plant components of A. scholaris were reported by Goyal et al (alkanes, alkanols, and sterols). The crude methanolic extracts of the leaves, stem, and root barks of A. scholaris were tested for antibacterial activity using petrol, dichloromethane, ethyl acetate, and butanol fractions. Khan et al. found that butanol fraction demonstrated a broad range of antibacterial activity.

Antioxidant

The compounds known as antioxidants work to neutralize the harmful effects of excess free radicals, reactive oxygen species, and nitric oxide. Natural antioxidants found in plants are a great source for lowering the risk of certain diseases like cancer, heart disease, and stroke. A. scholaris’s antioxidant activity has so far been investigated using in vitro research models. The antioxidant potential of A. scholaris has not been reported. According to James et al., the antioxidant activity of flower methanol extracts was higher than that of fruit. The phenolic and flavonoid content of leaves and the flavonoid content of flower and fruit extracts were attributed to the observed radical scavenging and antioxidant activity.