Euphorbia breviarticulata

Garden location: 17° 42′ 58.11″ N, 64° 49’47.51″ W

Common Name: False Cow Horn
Scientific Name: Euphorbia breviarticulata Pax
Family: Euphorbiaceae
Native Range: Eastern Africa, from Ethiopia and Somalia southward through Kenya to Tanzania; some references also include Uganda and South Sudan. It naturally inhabits dry shrubland, thorn scrub, sandy ground, rocky outcrops and remnants of coastal dunes.

General Description

Euphorbia breviarticulata is a large, perennial succulent shrub that normally branches from near the base. It may reach approximately 4.5 metres in height and can occasionally develop into a small tree approaching 6 metres.

Its thick, green, photosynthetic branches are usually three- or four-angled and divided by constrictions into short segments. The branch margins are strongly toothed and armed with paired spines. The plant is essentially leafless, relying upon its fleshy green stems for photosynthesis.

Phenological Markers

1. Vegetative Growth

What to look for:

• Pale green growth appearing at the tips of established branches
• Extension of existing stems
• Formation of new angular stem segments
• New lateral branches developing from older stems
• Young spines appearing softer and lighter in colour
• Gradual darkening and hardening of new growth

Because the plant is normally leafless, changes in its stems—not the production of leaves—provide the principal evidence of active vegetative growth.

2. Resting or Reduced-Growth Period

What to look for:

• Little or no extension at branch tips
• Mature stems retaining a uniform green or bluish-green colour
• New stem segments becoming firm and fully developed
• Spines darkening and hardening
• Temporary wrinkling or slight contraction of stems during prolonged drought

As a succulent adapted to dry environments, the plant may reduce visible growth during extended dry periods and resume growth after increased rainfall or irrigation.

3. Flower-Bud Development

The flowering structures develop near the upper margins or tips of mature stem segments.

What to look for:

• Small rounded swellings forming close to the spines
• Clusters of short flower stalks emerging from the stem margins
• Developing yellow or yellow-green structures
• Several buds forming together in compact groups

The structures commonly regarded as flowers in Euphorbia are actually specialized flower clusters called cyathia.

4. Flowering

What to look for:

• Clusters of small golden-yellow cyathia
• Cyathia occurring singly or in groups, commonly with several crowded together
• Yellow nectar glands becoming conspicuous
• Tiny male flowers producing visible pollen
• A central female flower extending beyond the surrounding structure
• Insects visiting the cyathia for nectar or pollen

The cyathia may be approximately 9 millimetres across and can occur in clusters of several individual flowering structures. Reports from cultivated plants commonly associate flowering with spring, but flowering in St. Croix may be influenced more strongly by local rainfall, irrigation and temperature than by a temperate-season calendar.

5. Pollination

What to look for:

• Bees, flies, wasps, moths or other small insects visiting the cyathia
• Pollen visible on visiting insects
• Repeated movement by insects between separate flower clusters
• The central female flower remaining after some male flowers have faded

The open, nectar-producing cyathia can attract a variety of insects. Record the visitor whenever possible, together with the time of day and weather conditions.

6. Early Fruit Development

After successful pollination, the ovary begins to enlarge above or beyond the cyathium.

What to look for:

• A small green, distinctly three-lobed swelling
• The developing fruit projecting outward on a short stalk
• Withering or disappearance of the surrounding floral structures
• Gradual enlargement of the three sections of the fruit

7. Maturing Fruit

What to look for:

• Capsules becoming more prominently three-lobed
• Fruit increasing to approximately 9 millimetres long and 18 millimetres wide
• Colour changing from green toward reddish or reddish-brown
• The fruit wall becoming firmer as the seeds mature

The mature fruit is a deeply three-lobed capsule containing pale grey, nearly spherical seeds.

8. Seed Maturity and Dispersal

What to look for:

• Capsules drying and becoming duller in colour
• Fine lines appearing where the three sections will separate
• Capsules splitting suddenly when fully mature
• Empty fruit stalks remaining after seed release
• Seeds found beneath or near the parent plant

As with many species of Euphorbia, the ripe capsule may split forcefully and scatter its seeds away from the parent plant.

9. Stem Ageing or Damage

Because this species does not have a normal seasonal leaf fall, ageing is most evident in its stems.

What to look for:

• Older stems becoming dull green, grey-green or corky
• Scarring around old flower and fruit positions
• Dead or damaged branch tips
• Yellowing, browning or collapse following excessive moisture
• Physical damage caused by wind or contact
• New growth emerging below a damaged section

Suggested Observation Schedule

Observe the plant at least once each month. During budding, flowering or fruit development, weekly observations will provide a more accurate record.

Record:

• Date
• Rainfall or irrigation since the previous observation
• New stem growth
• Presence of flower buds
• Number or abundance of open cyathia
• Insect visitors
• Developing green fruit
• Reddish or mature fruit
• Open or empty capsules
• Evidence of seed dispersal
• Stem damage, disease or dieback

Probable Sequence at the Garden

Rainfall or irrigation → new stem growth → flower-bud formation → open yellow cyathia → insect visitation → green three-lobed capsules → reddish mature capsules → capsule splitting and seed dispersal

The timing of this sequence should be treated as provisional until the Garden has accumulated observations over several years.

Important Safety Note

All parts of the plant contain milky latex. The sap can irritate or burn the skin and eyes and is poisonous if ingested. Gloves and eye protection should be used when handling damaged stems, flowers or fruit. The spines can also cause serious physical injury.