Hygrophila corymbosa ''Angustifolia''

Geographic Origin and Habitat: *Hygrophila corymbosa* var. 'Angustifolia' (formerly known in some forms as *Nomaphila stricta*) is an amphibious plant native to Southeast Asia, particularly Thailand, Malaysia, and Indonesia. In its natural habitat, it thrives along the banks of slow-moving rivers, shaded streams, and swamps, often emerging partially or completely during the dry season and then being completely submerged during the monsoons.

Taxonomy and Genetics: It is a dicotyledon in the Acanthaceae family. The epithet 'Angustifolia' (from Latin *angustus* = narrow and *folium* = leaf) describes its characteristic varietal mutation: leaves that are significantly longer and more lanceolate than the nominal form (*Hygrophila corymbosa*), which instead has much wider and oval leaf blades.

Physical Structure: It is a classic stem plant (caulescent). Its stems are robust, thick, rigid, and fleshy, capable of supporting themselves even out of the water. Adventitious roots often sprout from the nodes along the stem to anchor or draw extra nutrients. The leaves develop in opposite decussate pairs (rotated 90 degrees from the previous node) and are noticeably elongated (up to 15-20 cm) and narrow, resembling willow or oleander leaves.

Color and Texture: The coloration ranges from apple green to intense dark green. In the presence of very strong light, the central vein and upper surface may take on faint bronze or rust hues. The submerged leaf texture is smooth, while if grown emersed (paludarium), the leaves become leathery, covered with dense, fine fuzz (trichomes), and produce beautiful lilac or purple tubular flowers at the leaf axils.

Lighting and CO2: An extremely rustic and accommodating plant. It survives without problems under weak or medium lighting, but in these conditions it will tend to lose its lower leaves (which remain in the shade) and greatly elongate its internodes. With intense light, growth becomes very rapid and compact. It absolutely does not require carbon dioxide (CO2) supplementation to survive, although its addition increases growth rates tenfold.

Nutrition and Substrate: It feeds a rather deep and developed root network, therefore preferring a rich substrate (allophane soil or fertile bottom). However, the countless adventitious roots on the stem demonstrate its formidable ability to extract nutrients (especially nitrates and potassium) directly from the water column. It is an excellent consumer of pollutants, ideal for stabilizing newly established tanks.

Water Chemistry: One of the most tolerant aquarium plants ever. It adapts to acidic pH (6.0) as well as distinctly alkaline (8.0). It withstands very hard water (GH up to 20) and soft water, at temperatures between 20 and 28°C. It is highly indicated for community aquariums with livebearers or African Cichlids that are not too aggressive with vegetation.

Space Management and Placement: Its imposing size (it can easily exceed 50 cm in height) and long, drooping leaves make it perfect for the background or as a focal plant at the sides of the aquarium to hide filter pipes. Given the width of its canopy, the stems should be planted at least 4-5 cm apart to prevent the lower leaves from rotting due to lack of light.

Trimming: It grows incessantly towards the surface. When the stems bend on the water surface or emerge, pruning (topping) is mandatory. The stem is cut just above a healthy node. The rooted lower stump will quickly throw out two or more lateral shoots (making the bush thicker), while the removed upper part (apical cutting) can be buried to form an independent new plant.

Risks and Diseases: It is a very strong plant, but it has a chemical "Achilles' heel": it is extremely sensitive to Potassium (K) deficiency. If this macronutrient is scarce, older leaves will develop scattered small holes and the edges will quickly yellow due to necrosis (classic "pin-hole" symptoms). It is crucial to supplement with potassium-based liquid fertilizers to keep the leaves intact and lush.