Gratiola viscidula

Gratiola viscidula is a little-known species from the wetlands and boggy stream margins of the eastern United States, where it grows in nutrient-poor, acidic, cool-water habitats among mosses and sedges. Its leaves are small, lanceolate, and covered in fine glandular hairs that give them a slightly sticky texture — a trait unusual in aquatic plants and indicative of its preference for emergent or semi-emergent conditions in the wild. When cultivated submerged, it develops attractive, compact stems with closely spaced leaf pairs. The species has become something of a collector's plant in the advanced planted aquarium community because of its unique leaf texture and rarity in trade. It performs best in cool, soft, acidic conditions that exclude most tropical competitors, making it suitable for Appalachian biotope setups or paludarium environments. Gratiola viscidula requires stable water chemistry and is particularly sensitive to high pH and mineral hardness, which cause rapid leaf yellowing and stem die-back. It grows slowly relative to other stem plants, demanding patience and attentive husbandry from the keeper.

Placement Place in the midground or background of cool-water setups. Works well in paludariums at the water margin. In aquariums, keep away from high-flow areas that may stress delicate stems.

Lighting Moderate lighting (30–50 PAR) is preferred. Excessive light combined with warm temperatures leads to melt. A photoperiod of 8 hours is usually sufficient for steady growth.

CO2 & Fertilisation Low CO2 levels (10–15 ppm via injection) can help in soft-water tanks. This plant prefers nutrient-lean conditions; avoid heavy fertilisation. A light dose of micronutrients once weekly is adequate.

Propagation Stem cuttings of 5–8 cm root slowly over 2–3 weeks. Take cuttings from healthy, firm upper portions of the stem. Avoid disturbing the plant unnecessarily as it is sensitive to handling.

Trimming Trim gently every 3–4 weeks or as needed. Given its slow growth, over-trimming can set back recovery significantly. Remove yellowed or damaged leaves at the base promptly to prevent decay.