Yos
Sapium glandulosum
Native Region
Central and South America
Max Height
15-30 meters
Family
Euphorbiaceae
Conservation
LC
Uses
Distribution in Costa Rica
Legend
Elevation
0-1500m
Regions
- Limón
- Alajuela
- Heredia
- San José
- Puntarenas
- Guanacaste
Season
Flowering
Mar-Apr
Fruiting
Jun-Jul
Yos
Yos (Sapium glandulosum), also known as Leche de Vaca or Milkwood, is one of Costa Rica's most successful pioneer trees. Easily recognized by the distinctive glands at the top of its leaf stalks and the abundant milky latex that flows when any part is cut, this fast-growing species colonizes disturbed areas and provides critical food resources for wildlife. While it may not be the most glamorous rainforest tree, Yos is an ecological workhorse—one of the first trees to appear after disturbance and a favorite of seed-eating birds across its range.
Quick Reference
- Scientific Name
- Sapium glandulosum
- Family
- Euphorbiaceae (Spurge Family)
- Maximum Height
- 15-30 m
- Trunk Diameter
- Up to 60 cm
- Conservation
- Least Concern
- Key Feature
- Glands on petiole; milky latex
iNaturalist Observations
Community-powered species data
4000
Observations
186
Observers
📸 Photo Gallery
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Taxonomy and Classification
- Sapium: From Latin "sapere" (taste/sap) - referring to the latex - glandulosum: Latin for "full of glands" - the petiole glands - Family Euphorbiaceae includes rubber, cassava, poinsettia - Genus contains ~100 species with milky latex
Common Names
| Language/Region | Common Name(s) | Notes |
|---|---|---|
| Spanish (CR) | Yos | Most common name |
| Spanish | Leche de Vaca | Cow's milk - for latex |
| Spanish | Lechero | Milk-producing |
| English | Milkwood | For abundant latex |
| English | Glandular Sapium | Scientific translation |
| Trade | Various regional names | Varies by country |
Related Species in Costa Rica
| Species | Common Name | Habitat |
|---|---|---|
| Sapium macrocarpum | Yos Grande | Wet forests |
| Sapium laurifolium | Yos Laurel | Various forests |
| Hura crepitans | Javillo (related) | Same family, wet forests |
| Croton spp. | Targuá (related) | Same family, various |
Physical Description
Overall Form
Yos is a medium-sized tree with a typically straight trunk and a rounded, somewhat open crown. It's a fast-growing pioneer that can establish quickly in disturbed areas. The tree is semi-deciduous, dropping leaves briefly in the dry season in drier areas.
Identifying Features
The Diagnostic Glands
- Location: Top of leaf stalk (petiole)
- Number: Usually 2 prominent glands
- Color: Often reddish or dark
- Function: Attract ants (extrafloral nectaries)
- Key ID: Most diagnostic feature!
- Visible: Easy to see on fresh leaves
Latex
- Color: White, milky
- Flow: Abundant, quick
- Consistency: Thick, sticky
- Warning: Caustic—can irritate skin/eyes
Leaves
- Arrangement: Alternate, simple
- Shape: Elliptic to ovate
- Size: 8-15 cm long
- Margin: Finely serrated
- Tip: Pointed (acuminate)
- Texture: Somewhat leathery
Flowers and Fruit
- Flowers: Small, greenish, in terminal spikes
- Fruit: 3-lobed capsule, ~1.5 cm
- Seeds: Dark, 3 per capsule
- Dehiscence: Explosive, loud cracking
- Season: Mainly rainy season
Like many Euphorbiaceae, Yos produces copious milky latex that can cause serious irritation: Cautions: - Skin: Can cause rashes, burning - Eyes: VERY dangerous—can cause temporary blindness - Mouth: Highly toxic if ingested If Exposed: - Wash thoroughly with soap and water - For eyes, flush with clean water, seek medical help - Never burn branches near face (latex vaporizes) Working Safely: - Wear gloves when handling cut branches - Keep away from face when cutting - Avoid during hot weather (latex more fluid) The latex is a defense mechanism against herbivores—effective!
Distribution and Habitat
Global Distribution
Geographic Distribution
Distribution in Costa Rica
| Province | Abundance | Notes |
|---|---|---|
| Guanacaste | Common | Dry to wet transition zones |
| Puntarenas | Common | Pacific lowlands and slopes |
| Alajuela | Common | Northern lowlands to foothills |
| Heredia | Common | Sarapiquí, lower slopes |
| San José | Common | Valley edges, lower mountains |
| Limón | Common | Caribbean lowlands |
| Cartago | Present | Lower elevations |
Habitat Preferences
- Elevation: Sea level to 1,800 m
- Climate: Tropical dry to very wet
- Rainfall: 1,500-4,500 mm/year
- Habitat: Forest edges, secondary growth, pastures
- Light: Full sun to partial shade
- Soil: Adapts to many soil types
- Disturbance: Thrives in disturbed areas
Ecological Role
Pioneer Powerhouse
Succession Role
- Early colonizer: Among first trees after disturbance
- Fast growth: Rapid establishment
- Gap specialist: Thrives in forest openings
- Nurse species: Provides shade for slower species
- Nitrogen indifferent: Establishes on poor soils
Wildlife Value
- Seed-eating birds: Major food source
- Oropendolas: Favorite food
- Parrots and parakeets: Consume seeds
- Small mammals: Eat fallen seeds
- Ants: Attracted to petiole glands
Yos is one of the most important food sources for seed-eating birds in Costa Rica: Why Birds Love Yos: - Seeds rich in oils and proteins - Abundant fruit production - Predictable fruiting season - Accessible seed arrangement Regular Visitors: - Oropendolas (Montezuma, Chestnut-headed) - Parakeets (several species) - Toucans (occasionally) - Tanagers - Saltators - Various finches Fruiting Spectacle: When a Yos is in fruit, watch for mixed flocks gathering— sometimes dozens of birds feeding together! This makes Yos valuable for birdwatching locations and wildlife corridors.
Ant-Plant Relationship
Extrafloral Nectaries
Those distinctive glands at the top of the leaf stalks aren't just for identification—they're extrafloral nectaries: How They Work: - Glands produce sugary nectar - Ants feed on the nectar - Ants patrol the plant - Ants attack herbivorous insects Mutual Benefits: - Plant: Gets protection from herbivores - Ants: Get reliable food source - Neither can thrive as well alone Observable: Look closely at Yos leaves and you'll often see ants visiting the petiole glands—a mutualism in action!
Uses
Traditional and Modern Applications
| Use Category | Application | Notes |
|---|---|---|
| Wildlife value | Bird food source | Primary ecological value |
| Restoration | Pioneer plantings | Fast establishment |
| Shade | Pasture trees | Provides shade for cattle |
| Firewood | Fuel | Minor use |
| Traditional medicine | Various remedies | Latex used carefully |
| Historical | Latex extraction | Rubber substitute (minor) |
While Yos has traditional medicinal uses, the caustic latex makes it potentially dangerous: - Traditional uses: Warts, skin conditions (external) - Extreme care needed with any application - Internal use is dangerous - Modern alternatives usually preferred Do not attempt self-treatment with Yos latex!
Cultivation
Growing Yos
Identification Guide
How to Identify Yos
Primary Identifiers:
- Paired glands at petiole top (most diagnostic!)
- Abundant white latex when any part cut
- Serrated leaf margins
- 3-lobed seed capsules
Supporting Features:
- Medium-sized pioneer tree
- Forest edges and secondary growth
- Elliptic, pointed leaves
- Fast-growing habit
Where to See Yos in Costa Rica
| Location | Context | Notes |
|---|---|---|
| Throughout Central Valley | Forest edges, pastures | Very common |
| Sarapiquí region | Secondary forest | Abundant |
| Guanacaste roadsides | Pioneer growth | Common along roads |
| Osa Peninsula | Forest margins | Present |
| Caribbean lowlands | Secondary vegetation | Common |
Yos is one of the easiest trees to find in Costa Rica: Where to Look: - Forest edges everywhere - Secondary growth areas - Along rural roads - In pastures (often left for shade) - Recent clearings Identification Tips: - Look for paired glands on leaf stalks (easiest ID) - Break a small twig—abundant white latex flows - Listen for exploding seed capsules in fruiting season Best Time for Birds: - When fruiting (mainly rainy season)
- Morning hours - Look for mixed flocks feeding Yos is so common that once you learn it, you'll see it everywhere!
The Euphorbiaceae: A Family of Contrasts
The spurge family (Euphorbiaceae) is remarkably diverse, but almost all members share one trait: milky latex: Costa Rican Family Members: - Yos (Sapium) - This tree - Javillo (Hura) - Explosive sandbox tree - Croton (Targuá) - Many shrubby species - Manihot (Yuca) - Cassava, the food crop - Euphorbia - Poinsettias and spurges - Hevea - The source of natural rubber The Latex Defense: - Discourages herbivores - Quick-sealing wound response - Often contains toxic compounds - Varies in potency between species Economic Importance: - Natural rubber (Hevea) - Cassava (Manihot) - major food crop - Ornamentals (poinsettia, crotons) - Castor oil (Ricinus) Yos represents this important family in Costa Rica's forests!
External Resources
Community observations and photos
Botanical information
Regional botanical reference
References
📚 Scientific References & Further Reading
Burger, W. & Huft, M. (1995). Flora Costaricensis: Euphorbiaceae. Fieldiana Botany
Janzen, D.H. (1991). Historia Natural de Costa Rica. Editorial Universidad de Costa Rica
Stiles, F.G. & Skutch, A.F. (1989). A Guide to the Birds of Costa Rica. Cornell University Press
In a country famous for towering emergents, magnificent buttresses, and rare hardwoods, the Yos might seem unremarkable—a common tree found along every road and forest edge. Yet this milkwood pioneer is one of the unsung heroes of Costa Rica's forests. When a tree falls, when land is abandoned, when a gap opens in the canopy, Yos is among the first to arrive, quickly establishing and beginning the slow process of forest recovery. Its branches become feeding stations for dozens of bird species, its petiole glands sustain armies of protective ants, and its shade nurtures the seedlings of slower-growing species that will eventually overtake it. Every forest has to start somewhere, and more often than not, that somewhere includes Yos. Next time you pass by one of these common trees, take a moment to check those characteristic glands on the leaf stalks, maybe watch for a moment as birds feast on its seeds, and appreciate this humble workhorse of tropical forest succession.
