Phenology Walk – Bitter Ash

Bitter Ash (Quassia amara)

Family: Simaroubaceae
Origin: Native to the Caribbean, Central America, and northern South America
Garden location: 17° 42′ 55.88″ N, 64° 49′ 51.91″ W (Front 9)
ArbNet Level II list: Yes
POWO Status: Shrub or Tree
IUCN Red List threat level: Least Concern

What to watch for (Phenology)

Leaves

  • Leaf flush: Periodic through the year, often following rainfall
  • Leaf drop: Minimal; semi-evergreen to evergreen in St. Croix conditions
  • Notes: Leaves are pinnate, glossy, and visually delicate compared to many hardwoods

Flowers

  • Buds: Form in loose terminal clusters
  • First bloom: Often late spring into summer
  • Peak bloom: Early wet season; showy and noticeable
  • End of bloom: Gradual decline rather than abrupt finish
  • Pollinators observed: Bees and other nectar-feeding insects

Fruit / seed

  • Fruit set: After flowering
  • Ripening: Summer into fall
  • Dispersal: Birds; small dark drupes

Weather sensitivity

  • Rain-triggered? Yes — flowering and new growth often follow rain events
  • Drought response: Moderately tolerant once established
  • Other notes: Appears to respond more to moisture pulses than strict seasonal cues

Why this plant matters

Quassia amara is best known for its intense bitterness, a chemical defense that has made it one of the most important medicinal trees in Caribbean and tropical pharmacology. Phenologically, it offers a balance between subtle foliage and dramatic flowering, rewarding close observation. Its presence in the Garden connects living phenology to centuries of botanical medicine, experimentation, and trade.

Cultural and historical significance

Cultural uses

  • Medicinal bitterwood: Wood and bark traditionally used as a tonic, digestive aid, and anti-parasitic treatment
  • Insect deterrent: Extracts used historically as natural insecticide
  • Phytochemistry: Source of quassin, one of the bitterest natural compounds known
  • Caution: Strong medicinal potency; traditional use requires care and knowledge

St. Croix / Caribbean notes

  • Native to the region and historically valued in local and colonial herbal medicine
  • Part of a wider Caribbean tradition of plant-based remedies and pharmacopeia
  • Represents an important link between indigenous knowledge, colonial science, and modern pharmacology
  • Often planted in gardens as both a medicinal and ornamental species

My observations

  • First observed in project: (date)
  • Notable moments:
    • (YYYY-MM-DD) — Flowering flush following sustained rainfall
    • (YYYY-MM-DD) — Notable bitter scent or sap observation during handling
  • Questions / uncertainties:
    • Consistency of flowering cycles year to year
    • Variation in medicinal compound intensity between individuals

Photos

  • Whole plant / habit
  • Leaves (pinnate structure and texture)
  • Flower clusters (buds and open blooms)
  • Fruit (immature and ripe)
  • Bark and wood (noting color and grain)
  • Repeated phenology images from the same vantage point over time

Medicinal Uses

Quassia amara (Bitterwood) is traditionally used as a bitter tonic to stimulate appetite and digestion, treat fevers, malaria, and gastrointestinal issues like indigestion, constipation, and worms, and has shown potential in studies for anti-inflammatory, anti-diabetic, and anti-parasitic effects, including head lice and rosacea. Its active compounds, quassinoids, also give it insecticidal properties, used for repelling pests and denaturing alcohol. 

Traditional & Folk Uses

  • Digestive Aid: Stimulates appetite, saliva, and stomach acid for indigestion, anorexia, and constipation.
  • Fever & Malaria: Brewed as a tonic for fevers and historically used as an antimalarial, with compounds showing anti-malarial activity.
  • Parasites: Used as an anthelmintic (for intestinal worms) and shows potential against head lice.
  • Liver Support: Used for hepatic (liver) disorders.
  • Skin Conditions: Topical applications studied for rosacea, showing effectiveness similar to metronidazole. 

Other Potential Uses & Properties

  • Anti-inflammatory: Compounds show promise in reducing inflammation.
  • Anti-leukemic: Some extracts exhibit anti-leukemic and anti-tumor properties.
  • Insecticide: Used as a natural pesticide and repellent for insects like aphids and mites.
  • Cosmetics: Used in tonics and skin conditioners. 

How It’s Used

  • Tonic: Bark and wood are brewed into infusions or decoctions.
  • Powder: Bark powder mixed with warm water before meals.
  • Extracts/Tinctures: Used topically or orally, often diluted. 

Important Considerations

Scientific Evidence: While traditional use is extensive, more clinical research is needed for many uses, though topical applications for lice and rosacea show promise. 

Bitter Principle: Contains quassinoids, responsible for its intense bitterness and medicinal effects.

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