Hydrocotyle vulgaris

Geographical Origin and Habitat: Hydrocotyle vulgaris, commonly known as marsh pennywort or common pennywort, is native to a wide range that includes Europe, North Africa, and Western Asia. It is a typically riparian and semi-aquatic plant, growing spontaneously in damp and muddy environments such as lake shores, marshes, peat bogs, and slow-flowing ditches. Its ability to live both completely submerged and in emersed form on water-saturated soils makes it extremely versatile.

Taxonomy & Genetics: It belongs to the family Araliaceae (previously placed in Apiaceae). The generic name Hydrocotyle comes from Greek and means 'water cup', referring to the slight depression in the center of the round leaves. Genetics and morphology are stable; it is a resilient species equipped with a robust genome that allows it to adapt to cold and temperate climates, resisting harsh winter temperatures in outdoor ponds.

Physical Structure: It features a thin and flexible creeping stem or stolon that runs horizontally on the substrate or intertwines in the water. From each node of the stolon, anchoring roots and vertical petioles develop, bearing a single leaf at the apex. The leaves are peltate, meaning the petiole inserts exactly in the center of the lower leaf blade, giving the leaf its typical umbrella or circular shield shape.

Color & Texture: The leaves display a bright, uniform, and glossy green coloration. The upper surface is smooth and water-repellent, while the margins are slightly lobed or crenate. The texture is leathery in emersed growth and slightly thinner and more flexible in submerged growth. Under intense light, the leaf blade assumes an almost glassy and highly decorative appearance.

Lighting & CO2: Tolerates a wide range of light intensities, from medium to very high. Under intense light and CO2 injection, the plant maintains a very low and compact habit, creeping along the ground and creating a dense carpet. In low light conditions, the petioles tend to elongate significantly towards the surface, assuming a messy habit.

Nutrition & Substrate: It is not particularly demanding regarding the substrate, as it is able to absorb nutrients both from the roots that dig in and directly from the

Water Chemistry: It is an exceptionally tolerant plant. It can survive water temperatures between 4°C and 30°C, tolerating even harsh winters if planted in outdoor ponds. The ideal pH ranges from 5.0 to 7.5, with a tolerated water hardness (KH) of 0 to 15 dKH. It prefers clean water but tolerates moderate organic loads well.

Space Management & Placement: Perfect for the foreground and midground in the aquarium. Due to its creeping habit and rapid growth, it can quickly colonize large areas, intertwining with the layout. It is exceptional for paludariums, ripariums, and Wabi-Kusa, where it grows vigorously out of the water climbing on rocks.

Pruning: It is pruned simply by cutting unwanted stolons with sharp scissors. Frequent pruning helps to contain expansion and maintain a dense carpet. Portions of cut stolon containing at least one node with leaves and roots can be replanted elsewhere to propagate the plant.

Risks & Diseases: The main risk is uncontrolled growth that can suffocate slower neighboring plants. If nutrients are insufficient, the leaves tend to shrink and lose their typical green gloss. Submerged leaves can be subject to algae attacks if fertilization is not balanced or in the presence of stagnant water.