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Oroxylum indicum

Oroxylum indicum is a species in the monotypic Oroxylum of the family, commonly known as the Indian trumpet or broken bones due to its brittle branches. Native to subtropical and tropical regions of South and Southeast Asia, it typically grows 10–12 meters tall with a straight bole up to 40 cm in diameter, featuring soft, light brown or grayish bark and an open, irregular crown. The plant is characterized by its large, 2–3-pinnate leaves reaching 90–180 cm long with ovate or elliptic leaflets, showy reddish-purple to pinkish-yellow bell-shaped flowers that bloom in –, and distinctive flat, sword-shaped fruit capsules measuring 30–100 cm long containing winged seeds. Widely distributed from the Himalayan foothills through , , , , , , , , , , , , and southern , O. indicum thrives in lowland woodlands, moist forests, riverbanks, ravines, and hill slopes up to 1,200 meters elevation. It prefers damp, subtropical to tropical climates and is often found in secondary forests, clearings, and along roadsides, exhibiting fast growth and partial deciduousness in drier seasons. Ecologically, the tree supports by providing and is valued in for shade and . In , particularly , O. indicum holds significant ethnobotanical importance, with its roots, bark, leaves, flowers, and fruits used to treat ailments such as , , , ulcers, respiratory issues, and ; it is a key ingredient in formulations like Dashmula Churna. The plant is also cultivated ornamentally for its striking nocturnal flowers, which emit a musky scent, and its seeds yield oil for perfumery, while young leaves and fruits serve as vegetables in some regions. Ongoing pharmacological research highlights its bioactive compounds, including like , contributing to , , and potential anticancer properties.

Taxonomy and nomenclature

Classification

Oroxylum indicum belongs to the kingdom Plantae, phylum Tracheophyta, class Magnoliopsida, order Lamiales, family Bignoniaceae, genus Oroxylum, and species indicum. The genus Oroxylum is monotypic, containing only this species. Within the Bignoniaceae, O. indicum is classified in the tribe Oroxyleae, a small clade of four genera and approximately six species distributed in the Indomalaysian region. Molecular phylogenetic analyses place Oroxyleae as weakly supported sister to Catalpeae or to a broader clade including Catalpeae, the Tabebuia alliance, and paleotropical lineages, with closest relatives among genera such as Millingtonia (also in Oroxyleae), Catalpa, and Chilopsis (in Catalpeae). Historical synonyms for O. indicum include Bignonia indica L. and Spathodea indica Pers. The Oroxylum was originally described by Étienne Pierre Ventenat in 1808, with O. indicum designated as the based on material from .

The name Oroxylum is derived from words oros (mountain) and xylon (wood), alluding to the plant's frequent occurrence in hilly or mountainous regions or possibly to the quality of its wood. The epithet indicum is Latin for "of ," reflecting its native origin and early documentation from the . Common names for Oroxylum indicum vary widely across its range, often linked to its distinctive -shaped flowers, large pendulous pods, or traditional uses. In English, it is known as Indian trumpet flower or broken bones , the latter referring to the bone-like appearance of its fallen branches. In , it is called Shyonaka or Aralu, names used in Ayurvedic texts. Regional variants in include pheka in Thai and similar terms in and other local languages, highlighting its cultural recognition in and folklore. The plant was first described scientifically as Bignonia indica by Carl Linnaeus in 1753, based on specimens from India, and was later reclassified into the monotypic genus Oroxylum by Hermann Kurz in 1877 to better reflect its distinct morphological traits within the Bignoniaceae family. This taxonomic shift underscores the evolving understanding of its phylogenetic position, separating it from the broader Bignonia genus.

Botanical description

Growth habit and morphology

Oroxylum indicum is a fast-growing, lanky that typically attains a height of 10–20 meters, though specimens up to 27 meters have been recorded. It features a straight bole with a of 10–40 centimeters and develops an open, irregular due to its sparsely branched structure. The is or partly , depending on environmental conditions. The bark is thick, soft, and corky, often grayish-brown with prominent lenticels, while the wood is light and soft, historically utilized for lightweight applications such as matches and pulp production. The leaves are large compound structures, arranged in a pinnate fashion and reaching up to 2 meters in length, among the largest observed in dicotyledonous trees; they consist of 2–4 pinnate divisions bearing 15–25 ovate to oblong leaflets, each 4–11 centimeters long. Beneath the soil, O. indicum possesses a deep system that supports its rapid vertical growth and stability. The root bark is notably harvested for traditional medicinal purposes. In its life cycle, the tree exhibits rapid growth, achieving maturity within 5–7 years and reaching initial heights of 5–10 meters before significant branching occurs; it becomes partly during dry seasons, shedding leaves and remaining bare for several months.

Flowers, fruits, and reproduction

The flowers of Oroxylum indicum are large, measuring 7–10 cm in length, and exhibit a funnel-shaped (bell-shaped) with five reflexed lobes. They are reddish-purple outside and pale pinkish-yellow within, with a foul that attracts pollinators, and arise on pedicels 3–7 cm long. These blooms open nocturnally, facilitating (chiropterophily), as the species is self-incompatible and relies on cross- for successful reproduction, with open yielding up to 31.2% success rates in natural settings. The forms terminal racemes that can reach 40–150 cm in length, producing copious to support visitors during the extended flowering period of 6–8 weeks. This steady-state flowering enhances pollinator fidelity and geitonogamy avoidance in the bat-pollinated system. Fruits develop as woody, pendulous capsules that are strap- or sword-shaped, typically 30–120 cm long and 5–10 cm wide, containing numerous flat, ed seeds embedded in papery . The pods dehisce longitudinally upon maturity, releasing seeds primarily dispersed by due to their morphology, though dispersal may occur in riparian habitats; fruit set remains low at approximately 0.45% under natural conditions. Reproduction in O. indicum is predominantly sexual, occurring via seed propagation, with rates around 50% achieved in 19–25 days under optimal conditions such as pre-sowing soaking; vegetative propagation is possible through methods but rare in wild populations. Phenologically, flowering is often triggered by in the (March–May in some regions, extending to July–August in others), with fruit maturation following post-monsoon in the rainy season, ensuring aligns with favorable moist conditions for establishment.

Distribution and ecology

Geographic range

Oroxylum indicum is native to the , including , , , , and , as well as encompassing , , , , , , , and the , and extending to southern . Within its native range, the species occurs in the foothills of the , across Indochina, and in the region. Specific populations are documented in areas such as in , ; Cat Tien National Park in ; and forests across in southern . The plant has been introduced and cultivated in various tropical regions outside its native distribution for ornamental and medicinal purposes, though it remains primarily associated with its original Asian habitats. Historical evidence from ancient Ayurvedic texts indicates that Oroxylum indicum has been present and utilized in for millennia, underscoring its long-standing distributional stability in the region.

Habitat preferences and ecological interactions

_Oroxylum indicum thrives in tropical forests, along riverbanks, and in moist valleys, where it occupies damp, shaded understories and open clearings. It prefers well-drained loamy soils that are fertile and moisture-retentive, with tolerances for light to medium textures and slightly acidic to neutral levels. The species is commonly found at altitudes ranging from to 1,200 meters, often on slopes and in ravines within the Himalayan foothills, Eastern and , and . These habitats typically receive annual rainfall between 850 and 1,300 millimeters, supporting its growth in subtropical to tropical climates. Once established, O. indicum demonstrates moderate , retaining foliage in drier periods, though it requires consistent moisture during early growth stages. It is sensitive to and temperatures, limiting its persistence in regions with winter freezes, and is best suited to warm, humid environments without prolonged dry spells. Flowering occurs from to in response to onset, aligning with seasonal moisture availability. Ecologically, O. indicum engages in symbiotic associations with actinomycetes, particularly Pseudonocardia oroxyli, which colonizes zones and may contribute to health through activity. is primarily facilitated by fruit bats of the Pteropodidae, attracted to the nocturnal, foetid-scented flowers that produce abundant and ; these bats promote via trap-line foraging behaviors. The tree also hosts fungal pathogens, though specific interactions remain understudied in natural settings. In its ecosystem, O. indicum serves as a pioneer species that provides shelter and foraging resources for various wildlife, including birds and insects, while its wind-dispersed winged seeds aid in forest regeneration. Decaying leaf litter from the tree enriches soil organic matter, enhancing nutrient cycling and fertility through contributions of nitrogen and minerals, which support understory vegetation and microbial communities. These roles underscore its importance in maintaining biodiversity in tropical forest understories.

Conservation status

Population status and threats

Oroxylum indicum has not been globally assessed by the ( as of 2024). However, regional assessments indicate significant population declines in parts of its range, particularly in , where it is considered vulnerable or threatened in several states due to localized pressures. The species faces primary threats from overharvesting of its roots and bark for traditional medicinal uses, which has contributed to population declines in some areas over the past few decades. Habitat loss driven by , , and has further fragmented distributions, with sparse wild populations reported in northern , where tree densities remain low (e.g., basal areas of 0.1–0.63 m²/ha in and forests). Overgrazing and forest fires compound these issues, limiting regeneration in accessible habitats. In and , populations are particularly vulnerable owing to high medicinal demand, resulting in fragmented and declining stands outside protected areas. It is also considered threatened in Nepal due to unsustainable collection and . Overall data on trends remain limited.

Protection and cultivation efforts

Oroxylum indicum is recognized as vulnerable in several Indian states through Conservation Assessment and Management Prioritisation () workshops, including , , , , , , , , , , and , prompting targeted regional protections under national medicinal plant conservation frameworks such as those overseen by the National Medicinal Plants Board. Although not listed under the Convention on International Trade in Endangered Species (), the species benefits from broader Indian policies aimed at conserving threatened medicinal flora, including restrictions on in forest areas. In-situ conservation efforts focus on protecting natural populations within protected areas, such as in , , where the species occurs in forest biomes and contributes to preservation initiatives. Similarly, specimens are documented in Cat Tien , , supporting ecosystem-based management in lowland tropical forests. Ex-situ strategies include and maintenance at institutions like the , Central Regional Centre in Allahabad, where root suckers have been used to establish experimental gardens for long-term preservation. Seed banking efforts leverage the species' storage behavior, enabling viability retention for years under controlled conditions to support conservation. Cultivation practices emphasize to reduce pressure on wild populations, with seeds achieving up to 73% through , followed by transplanting seedlings spaced 5-6 meters apart after 4-5 months in polybags. Vegetative methods using hardwood cuttings treated with auxins like NAA or IBA also succeed, offering alternatives for clonal in systems. Sustainable harvesting guidelines promote substituting destructive root collection with harvesting from branches or leaves, which contain comparable bioactive compounds, as outlined in operational manuals for non-timber forest products. Recent advancements include cryopreservation protocols using , achieving high viability post-storage to preserve nuclear , as developed by Harsha and Rajasekharan in 2023. Community-based programs in , such as those involving local ethnic groups in and , integrate cultivation and awareness for sustainable use, with explorations documenting low-density populations to guide on-farm propagation from 2010 onward. These efforts face challenges like low public awareness of the ' status and ongoing illegal trade driven by medicinal demand, which undermine wild populations despite available alternatives.

Phytochemistry

Major chemical constituents

Oroxylum indicum is rich in bioactive compounds, with representing the predominant class of phytochemicals across various plant parts. The primary include oroxylin A (a key baicalein derivative), , , and prunetin, which are structurally characterized as flavones and . Oroxylin A, chemically 5,7-dihydroxy-6-methoxyflavone, is notably concentrated in the stem bark and fruits, while (5,7,2',6'-tetrahydroxyflavone) predominates in the root bark and seeds. (5,7-dihydroxyflavone) occurs widely in the bark and seeds, and prunetin (5,7-dihydroxy-4'-methoxyisoflavone) is found in the heartwood. These contribute to the plant's chemical profile, with total flavonoid content ranging from 2% to 15% of dry weight, depending on the solvent and plant part; for instance, methanolic extracts of seeds can yield up to 11.6% . Concentrations of these are highest in seeds and root bark, often reaching 5-10% dry weight collectively. alone has been quantified at approximately 3.95% dry weight in root bark extracts, highlighting its abundance in these tissues. Glycosylated forms, such as baicalein-7-O-glucoside (oroxin A) and baicalein-7-O-diglucoside (oroxin B), are also prevalent in seeds, comprising significant portions of the fraction. Beyond , Oroxylum indicum contains other notable compounds distributed across its parts. , a compound, is present in , while emodin (an ) occurs in the . , a , is found in the heartwood and , alongside (particularly ) in high levels in the . Trace alkaloids are reported in the , , and , though their specific identities remain less characterized. These compounds vary in distribution, with oroxylin A enriched in fruits and localized to . Identification and quantification of these constituents typically involve advanced analytical techniques such as (HPLC) coupled with (MS) for separation and detection, and (NMR) spectroscopy for structural elucidation. HPLC-MS assays have enabled precise measurement of major like (0.09-0.18% in seeds) and , with total content varying by solvent—e.g., higher yields in versus . These methods confirm the chemical inventory and support in studies. The composition of major chemical constituents in Oroxylum indicum exhibits variability influenced by geographic origin and seasonal factors. Samples from populations often show elevated antioxidant-related compounds compared to those from , potentially due to edaphic and climatic differences; for example, root extracts from Indian sources have demonstrated higher total and levels in comparative assays. Seasonal harvesting also affects yields, with post-monsoon collections yielding higher concentrations in some studies. Such variations underscore the importance of standardized sourcing for consistency.

Biosynthesis and extraction methods

The biosynthesis of flavonoids in Oroxylum indicum primarily occurs through the phenylpropanoid pathway, a key metabolic route in that converts into various . This pathway involves the initial of by (PAL) to form , followed by subsequent and steps leading to flavonoid precursors. Transcriptomic analyses of O. indicum roots have identified genes associated with the pathway, including chalcone synthase (CHS) and flavone synthase (FNS), with differential regulation observed across developmental stages. In O. indicum , which are a primary site for accumulation, synthesis is linked to the , where aromatic amino acids like serve as precursors for hydrolyzable that hydrolyze to form . This process is more pronounced in compared to aerial parts, with exhibiting higher concentrations of and related such as and . Environmental stressors, including elicitors like silver nanoparticles or wounding, upregulate the expression of pathway genes, enhancing production as a defense mechanism; for instance, such stresses have been shown to increase yields in cultured tissues. Extraction of bioactive compounds from O. indicum traditionally relies on solvent-based methods, where or extracts from and seeds yield 10-20% of total , depending on solvent polarity and extraction time. For example, ethanol-water bath from seeds achieves higher recovery of oroxylin A and compared to water alone. Advanced techniques like supercritical CO₂ extraction target non-polar efficiently, offering solvent-free alternatives with yields comparable to conventional methods while minimizing degradation. Ultrasound-assisted (UAE) has been optimized for , using statistical designs to achieve up to 15% higher recovery in shorter times (e.g., 30 minutes at 40 kHz), promoting by reducing energy use. Recent profiling in 2025 demonstrated that stability in preserved O. indicum tissues is maintained longer in dried or aged samples, with retaining up to 80% of initial levels after one year of under controlled conditions, aiding post-harvest . To support efforts, stems and small branches are viable substitutes for in extraction protocols, as comparative chemo-profiling shows similar profiles (e.g., content within 10% variance), reducing pressure on wild populations without compromising yield.

Uses and pharmacology

Traditional medicinal applications

In Ayurveda, Oroxylum indicum is known as Shyonaka and serves as a key component of Dashamula, a group of ten roots employed in tonics and formulations such as Dashamularishta for treating conditions like fever, , and . The root bark is traditionally used to address and gastrointestinal disorders, while seeds are administered as a powder at a dosage of 3-6 grams for and as a purgative. Leaves and fruits are prepared as decoctions for rheumatic pain, , and gastropathy, with the plant's properties supporting its role in managing vomiting, colic, and wounds. In , the plant is referred to as Mu Hu Die, primarily utilizing the seeds in decoctions to treat respiratory ailments including , , , and pertussis. Across Southeast Asian ethnomedicinal practices, the is applied as a for and skin conditions, while decoctions of the root and stem address gastrointestinal issues such as and . In Kannada folk medicine, the fruit is used in preparations to support urinary disorders and . Common preparations include powders from seeds and bark, pastes from bark for topical application on wounds and inflammation, and oils such as Narayana Taila infused with roots for joint pain and . These uses are documented in ancient texts like the (circa 300 BCE), where Shyonaka is recommended for , non-healing ulcers, and gynecological disorders.

Modern pharmacological research

Recent pharmacological studies on Oroxylum indicum have explored its therapeutic potential through , , and approaches, primarily focusing on extracts from leaves, roots, stems, and seeds. These investigations, conducted post-2020, highlight bioactive such as , oroxylin A, and as key contributors to its effects. Research emphasizes mechanisms underlying , activity, and anticancer properties, with preliminary evidence supporting low profiles. In neuroprotective research, leaf extracts of O. indicum have demonstrated attenuation of β-amyloid (Aβ)-induced neurotoxicity in SH-SY5Y cell models of Alzheimer's disease. At concentrations of 25–50 μg/mL, the extract reduced reactive oxygen species (ROS) levels, malondialdehyde production, and caspase-3 expression while enhancing antioxidant enzymes like superoxide dismutase and catalase. Root extracts similarly inhibited Aβ aggregation (IC₅₀: 11.47 μg/mL) and BACE1 expression in hydrogen peroxide-challenged SH-SY5Y cells, protecting against oxidative damage. Baicalein, a major constituent, further mitigates oxidative stress in vitro by scavenging ROS and upregulating anti-apoptotic pathways, with an antioxidant IC₅₀ of 19.08 μM in DPPH assays. Anti-inflammatory and antioxidant effects are attributed to that suppress the signaling pathway, reducing pro-inflammatory cytokines like TNF-α and IL-6. Stem extracts exhibited potent antiglycation activity, inhibiting advanced glycation end-product formation relevant to complications. These properties align with broader antioxidant capacities observed in leaf and pod extracts, which elevate total phenolic content. Anticancer investigations reveal oroxylin A's role in inducing , particularly in Epstein-Barr virus (EBV)-associated . studies (2024) showed baicalein binding stably to EBV proteins (e.g., dUTPase) and NPC targets like and , promoting with binding energies below -8 kcal/mol. Additionally, hydro-alcoholic extracts stimulated immune responses in RAW264.7 and THP-1 cells, enhancing TNF-α secretion (up to 98 pg/mL at 200 μg/mL) and exhibiting against lines, supporting immuno-stimulatory effects in models. Other antiviral studies corroborate O. indicum's inhibition of EBV replication in NPC contexts through dual targeting of viral and host proteins. assays using leaf extracts demonstrated accelerated contraction in excisional models (3% topical application, p < 0.05 by day 8), attributed to promoting migration. trials employed dosages of 100–500 mg/kg orally, showing efficacy without adverse effects. Safety profiles indicate low , with acute oral LD₅₀ exceeding 5000 mg/kg for ethanolic extracts in mice and no subacute effects at 250 mg/kg/day for 28 days in rats. A completed in 2021 using 1000 mg/day Sabroxy® extract for reported no significant adverse events.

Culinary and cultural applications

In , particularly in and , the young leaves, flower buds, and shoots of Oroxylum indicum are commonly consumed as , often stir-fried or boiled to accompany dishes. The large, immature pods, known locally as "lin mai" or "lin fa" in regions like Loei, , are harvested and grilled over before the tender inner seeds are scraped out and eaten raw or mixed with chili-based sauces such as laap. Flower buds are sometimes boiled and pickled, especially among ethnic groups like the Karen in . In , including , the young shoots are boiled and eaten as a simple , while immature pods and fruits are incorporated into curries or boiled with for everyday meals. The unripe seeds may be grilled and seasoned with spices for a flavorful , adding a mild, nutty taste to local cuisines. The light, soft wood of O. indicum finds practical use in rural tropical regions for crafting handles, agricultural implements, and components of carts due to its workability despite limited durability. The bark, rich in , yields a traditionally applied to and fabrics, and the also support processing in artisanal . The long, flat, sword-shaped pods are occasionally utilized in local crafts, such as decorative items or playthings mimicking swords, leveraging their distinctive form. As an , O. indicum is planted in tropical and subtropical gardens for its striking large leaves, trumpet-like flowers, and dramatic pendulous pods, which create a bold, irregular canopy. In some areas, it serves as a plant in tropical landscapes, providing both aesthetic appeal and functional screening. Additional utilitarian applications include the use of leaves as for during dry seasons, offering a nutritious when other is scarce. Sustainable harvesting of pods and leaves aligns with efforts, promoting non-destructive collection to support both local economies and wild populations.

Cultural significance

Role in mythology and folklore

In the oral traditions of the tribe of the , Oroxylum indicum holds a prominent place in their creation mythology. According to Onge lore, the spirit Eyuge fashioned the first human, named Onge, from the wood of this tree, establishing it as a sacred source of life and material for constructing shelters and canoes. In Javanese cultural narratives, the long, sword-shaped pods of O. indicum symbolize protection and heroism, inspiring the crafting of keris buah beko daggers modeled after their form, which are believed to ward off evil in traditional stories. This association echoes broader Southeast Asian where the tree's nocturnal flowers, pollinated by bats, are associated with renewal, particularly in Thai narratives. Within folklore, O. indicum, known as Shyonaka, is tied to concepts of divine longevity in ancient Hindu texts like the , where related herbs are invoked in hymns for rejuvenation and protection against ailments, reflecting its revered status among gods and sages.

Uses in rituals and art

In various Buddhist traditions across the Himalayan region, the seeds of Oroxylum indicum are strung together to create ceremonial decorations such as offerings to deities during religious rituals. These lightweight, papery-winged seeds are valued for their symbolic purity, as the plant's flowers bloom nocturnally and shed before dawn, evading insect contact, making them essential in auspicious ceremonies in . In , particularly among Buddhist communities, the seeds are similarly employed in offerings to gods and goddesses, reflecting the plant's sacred status in local spiritual practices. In , the plant, known locally as Pougorip or Totola, features in shamanic rituals performed by the Mun to invoke supernatural forces, underscoring its role in ceremonial contexts independent of monastic influences. Among the of , the seeds—termed ko ko mhendo or heart flower—are integral to cultural rituals and have inspired artistic expressions, such as the creation of sacred handmade paper and slates used to depict historical narratives of community trauma and resilience. Artistically, the bark of O. indicum yields natural dyes suitable for coloring fabrics, producing hues that align with traditional textile practices in , such as those documented in Thai dyeing techniques. The plant's distinctive long, pendulous fruits and bold foliage also render it a popular ornamental in tropical gardens, where its form contributes to artistry. Additionally, the seeds have been utilized decoratively to line traditional hats and reinforce structures in Himalayan crafts, blending utility with aesthetic appeal.