Sagittaria montevidensis - Giant Arrowhead

The Sagittaria montevidensis, also known as Montevideo Arrowhead, is a perennial aquatic plant that thrives in shallow areas of aquatic environments, particularly at a water depth between 5 and 20 cm. Its arrow-shaped leaves, characteristic of its botanical genus, distinguish it by its exceptional flowers. Its magnificent white flowering adorned with a purple-red heart, which extends from late spring to late summer, brings a touch of purity and elegance to the water's surface. It effortlessly enlivens aquatic scenes with lush foliage and large, wind-blown stems.

The Sagittaria montevidensis, more commonly known as Montevideo Arrowhead or Argentine Water Arrowhead, belongs to the family Alismataceae. This family encompasses herbaceous plants, mostly perennial and rhizomatous, adapted to aquatic environments in temperate, subtropical, or tropical regions. Native to South America, the Sagittaria montevidensis is found in Argentina, Bolivia, Chile, Ecuador, Brazil, Mexico, Peru, and, of course, Uruguay, particularly in the province of Montevideo, where it grows along the many small coastal rivers in the region. It thrives along watercourses, in mudflats, as well as on riverbanks and lake shores.

This herbaceous perennial plant, with underground rhizomes, forms a clump reaching a height of 0.50 to 0.90 m and consists of deciduous foliage arranged in a rosette. Submerged leaves are ribbon-like, while emergent leaves are shaped like arrowheads and smooth, measuring 20 to 30 cm long and up to 23 cm wide, rising on a long cylindrical and spongy petiole that can reach 75 cm long. Flowering occurs from June to September, and the flowers emerge from the vegetation on floral stems shorter than the leaves and trailing. The flowers, arranged in whorls or pairs at the nodes, have a 2 to 3 cm diameter. They contain three white petals marked with a wine-coloured spot and three green sepals. Each flower bears 12 stamens with yellow anthers. Pollination is carried out by insects, leading to the formation of a small capsule containing the seeds. These seeds are dispersed by water or attached to animals' hair, legs, or feathers. The seeds easily spread in mild climates.

The Montevideo Arrowhead, modest in appearance, offers particularly charming small flowers. Although it is affected by frost every winter, it regrows late from the stump in hotter climates. Therefore, in mild climates, it can be planted in open ground, but in cooler climates, pot cultivation is preferable. It thrives ideally in ponds and artificial pools submerged in water with a depth ranging from 5 to 20 cm. It thrives in full sun or slightly shaded areas in various soil types, whether acidic, slightly alkaline, or neutral, as long as they are rich in humus. For a balanced composition, combine Sagittaria montevidensis with plants suitable for riverbanks and shallow areas, such as Juncus inflexus, Asclepias incarnata, Lobelia cardinalis, Iris versicolor, Iris pseudacorus, Cyperus papyrus Cleopatra, Thalia dealbata (Water Canna), Iris pseudacorus Crème de la Crème (Yellow Flag Iris), and wetland grasses like Carex pendula, Cotton Grass (Eriophorum angustifolium), or Milium effusum ‘Aureum’.
To control the plant's seed propagation, it is advisable to prune the inflorescences once they have dried.