Seabeach Amaranth

Seaside spurge (Chamaesyce polygonifolia) is a close vegetative associate of seabeach amaranth. These two species share a low growth form and reddish stems. However, the leaves of seaside spurge are lighter green, more elongated, and less shiny than seabeach amaranth. 

Seabeach amaranth shows good reproductive success in the years when no major storm events occur. Seed output is correlated with plant size, with large plants estimated to produce several thousand fertile seeds over the course of a growing season. Based on the morphology of the flower and inflorescence, seabeach amaranth is considered to be wind-pollinated. Based on observed seed production by single isolated individuals, it is clear that seabeach amaranth is capable of self-pollination. 

Seabeach amaranth seems to "hedge its bets" with regard to seed dispersal, which is primarily via wind and water. To increase the odds that at least some of its offspring are likely to end up in  favorable habitat in future years, this species employees a three-part strategy of long-distance dispersal, short-distance dispersal, and "planting." Long-distance dispersal is achieved by some seeds that detach from the parent plant but remain in low-density capsules called utricles, which also include an air pocket. Borne by wind and currents, seed-filled utricles are able to disperse across inlets and long stretches of unsuitable habitat. Long-distance dispersal probably takes place primarily during storm events such as fall hurricanes and winter northeasters. Short-distance dispersal is achieved by other seeds that are released from the utricle as it becomes split or abraded by sand. These "naked" seeds are also dispersed by wind but to a much lesser degree than utricles, behaving like large, low-density sand grains. Naked seeds typically remain in the lee of the parent plant or get deposited in a nearby depression, usually within 300 feet of the parent plant. Seeds may often be observed to pile up around the bases of the parent plants, particularly larger individuals. Finally, some seeds remain within the utricle and attached to the plant and are never dispersed, getting "planted" as the dead or dying parent plant is buried by blowing sand at the end of the season.

The maximum lifespan of a seabeach amaranth plant is about 8 months, though many plants do not persist that long. This species overwinters as seeds, which are believed to be capable of persisting in the beach environment for many years until suitable conditions for gemmation are present.  

Upon germinating, seabeach amaranth initially forms a small reddish, upright spring. Soon the seedling begins to branch into a low-growing rosette consisting of 5 to 20 branches and typically reaching 4 to 12 inches in diameter. Occasionally a plant may reach a yard or more across, with a hundred or more branches. The stems are fleshy and pink-red or reddish, with small rounded leaves. Clustered toward the tip of the stem, the leaves are somewhat shiny, spinach-green in color, and have a small notch at the tip. Small white flowers and dark seeds are located in inconspicuous clusters along the stems. As they age throughout the fall, plants often turn reddish or purplish, and some stems and leaves may die back.

Seabeach amaranth germination takes place over a relatively long period, beginning as early as April in the south and starting in mid-May or early June farther north. Germination continues at least through July. Flowering begins as soon as plants have reached sufficient size, sometimes as early as June in the Carolinas but more typically commencing in July. Flowering continues until the plant dies in late fall or early winter. Seed production begins in July or August and reaches a peak in most years in September; seeding likewise continues until the plant dies. Seabeach amaranth plants that are not lost to burial or flooding from fall storms may persist through November in the north, and into January farther south. 

Seabeach amaranth occurs on barrier beaches, where its primary habitat consists of overwash flats at the ends of islands that are accumulating more sand and lower developing dunes and upper strands of non-eroding beaches. It occasionally establishes small temporary populations in other habitats, including sound-side beaches, overwash areas in developing dunes, and sand and shell material placed as beach replenishment or dredge spoil. Seabeach amaranth appears to be intolerant of competition and does not occur on well-vegetated sites. The species appears to need extensive areas of barrier island beaches and inlets that are not stabilized by perennial vegetation. These characteristics allow it to move around in the landscape as a fugitive species, occupying suitable habitat as it becomes available. The species is an effective sand binder, building small dunes where it grows. 

Seabeach amaranth has stems that are fleshy and pinkish-red or red, with small, rounded leaves that are 0.5 – 1 inch (in) (1.3 - 2.5 centimeters; cm) in diameter. The leaves, with indented veins, are clustered toward the tip of the stem and have a small notch at the rounded tip. Flowers and fruits are relatively inconspicuous, borne in clusters along the stems. Germination occurs over a relatively long period of time, generally from April to July. Upon germination, the species forms a small unbranched sprig, but soon begins to branch profusely into a clump. This clump often reaches 30 cm in diameter and consists of five to 20 branches. Occasionally, a plant may grow as large as a meter or more across.