Tropical milkweed, scientifically known as Asclepias curassavica, is frequently grown in gardens for its vibrant appearance and appeal to pollinators. Though native to the American tropics, this species is widely planted globally, often outside its natural range, where it can be confused with native North American milkweed species. Focusing on the plant’s structure, foliage, and reproductive parts provides a clear guide for accurate identification within the genus Asclepias.
Overall Structure and Growth Habit
Tropical milkweed is an erect, perennial subshrub, woody at the base, which remains evergreen in frost-free regions. In temperate zones, it is usually cultivated as an annual, dying back with a hard freeze. The plant typically reaches a height between two and four feet, growing on simple or branched stems. The stems are generally smooth and round, displaying a dull green color, often subtly suffused with dull red or purple tones, especially near the base. This upright habit makes it a prominent feature in garden beds.
Identifying Features of Leaves and Stems
The foliage of A. curassavica has distinct features. Leaves are arranged oppositely along the stem, emerging in pairs directly across from one another. They are characterized by a narrow, lanceolate, or oblong-lanceolate shape, tapering to a point at both the base and the tip. These leaves are typically medium to deep green and feature a smooth, non-fuzzy surface. Attached by short petioles, they measure between five and fifteen centimeters long and sometimes exhibit a noticeable white midrib. Like all milkweeds, the stems and leaves contain a milky white sap, or latex, that exudes when the tissue is damaged.
The Distinctive Flowers and Seed Pods
The most definitive feature of tropical milkweed is its unique flower structure and vivid coloration. Flowers are grouped in dense, rounded, flat-topped clusters called umbels, appearing at the tips of the stems or in the leaf axils, with each cluster containing six to twenty individual flowers. The individual flowers display a sharp contrast between the corolla (petals) and the corona (the central, crown-like structure).
The five corolla lobes are usually bright scarlet, red, or deep orange, and are typically reflexed (bent backward). This vibrant backdrop contrasts with the five cup-shaped corona lobes, or hoods, which are generally bright yellow or orange. Following pollination, the plant produces follicles (seed pods). These pods are fusiform (spindle-shaped), long, narrow, and held erect. They are smooth or only slightly pubescent, contrasting with the hairier pods of some native milkweeds. When mature, the pods turn brown and split open lengthwise to release numerous flat, ovate seeds. Each seed is attached to a tuft of fine, silky hairs (the pappus), which aids in wind dispersal.
Quick Visual Checklist for Identification
Accurately identifying tropical milkweed relies on observing the combination of its most visible traits. These features collectively confirm the plant’s identity as Asclepias curassavica.
Key Identification Traits
- Look for an overall upright, somewhat woody plant structure that reaches two to four feet in height.
- The foliage should be smooth, deep green, and slender, with leaves arranged in opposite pairs along the stem.
- The flowers provide the clearest visual confirmation, defined by a stark contrast between a red or scarlet corolla and a bright yellow or orange corona, all grouped in dense, rounded terminal clusters.
- Finally, the resulting seed pods are long, smooth, and upright, distinct from the shorter or hairier pods of many native varieties.