Ludwigia Arcuata

Overview and Taxonomy

Ludwigia arcuata is a species of flowering plant in the evening primrose family (Onagraceae) . It was first formally described by Thomas Walter in his 1788 publication, Flora Caroliniana .

• Scientific Name: Ludwigia arcuata Walter 

• Common Names: It is widely known as Piedmont primrose-willow in its native range . In the aquarium trade, it is frequently called Narrow Leaf Ludwigia or Needle Leaf Ludwigia due to its fine foliage . One source also mentions the name "Small Red Berry" .

• Family: Onagraceae 

• Synonyms: Over time, it has been reclassified, with homotypic synonyms including Isnardia arcuata and Ludwigiantha arcuata .

 Physical Description

This plant is a perennial herb that displays different growth forms depending on its environment .

• Growth Habit: It can be prostrate and creeping (growing along the ground and rooting at its nodes), often forming mats, or decumbent to ascending (lying on the ground but with upright tips) . When grown underwater in an aquarium, it adopts a more upright, ascending growth habit .

• Stems: The slender, reddish stems are slightly ridged, well-branched, and can reach 5-70 cm (about 2-27.5 inches) in length, growing up to 50 cm or more in aquatic settings .

• Leaves: The leaves are one of its most distinctive features. They are opposite, simple, and can be lanceolate (lance-shaped) to very narrowly linear (needle-like) .

  • Emerged/Emersed Leaves: On stems growing out of the water, leaves are typically narrowly elliptic to linear, measuring 0.6-1.8 cm long and 0.2-0.5 cm wide .

  • Submersed Leaves: When grown underwater, the leaves become longer and narrower, reaching 1.9-4 cm in length but only 0.1-0.25 cm wide, which gives the plant its "needle leaf" appearance .

  • Color: The foliage color is highly variable. It is generally green but can turn beautiful shades of yellow, orange, or brick red to red-brown under strong lighting, especially in submersed forms .

• Flowers: The plant produces showy, bright yellow flowers on emergent stems .

  • They are formed in the leaf axils (where the leaf meets the stem) and have four yellow petals (7-11 mm long) and four small, pointed green sepals .

  • The flowers are among the largest in its section and are primarily outcrossing, attracting insect visitors .

  • The flowering period is typically from spring to late summer (March to September) .

• Fruits and Seeds: The fruit is a hard-walled, club-shaped (clavate) capsule (5.5-10 mm long) that contains numerous small seeds .

 Native Habitat and Distribution

• Native Range: As confirmed by multiple authoritative sources, Ludwigia arcuata is native to the southeastern United States .

• Detailed Distribution: Its native range is primarily in the coastal plains, specifically in the states of Alabama, Florida, Georgia, and South Carolina .

• Habitat: In the wild, it is found in wet, sunny areas such as roadside ditches, edges of lakes and ponds, swampy prairies, springs, and sandy or mucky shorelines . It thrives in shallow, still or slow-moving water .

 Cultivation and Uses

Ludwigia arcuata is highly prized in the aquarium hobby and for water gardens due to its fine texture and vibrant colors .

• Aquarium Trade: It is a popular stem plant for aquascaping, where its needle-like leaves provide contrast against broader-leaved plants .

• Color Requirements: To achieve the intense red coloration that makes it so desirable, the plant requires high levels of lighting . In lower light, it will remain green. Nutrient levels, particularly low nitrogen and adequate iron and phosphorus, also influence the shift from green to red .

• Growth Conditions: It has a moderate growth rate and is considered relatively easy to care for with the right conditions .

  • Light: Prefers moderate to high light. Full sun is ideal for emersed growth .

  • Water: Temperature should be maintained between 20-28°C (68-82°F) , with a pH of 5.5-8.0 .

  • Substrate: Benefits from a nutrient-rich substrate to support root feeding .

  • CO2: While not strictly necessary, CO2 injection can significantly improve growth and color, especially in high-light setups .

• Propagation: It is very easy to propagate. Simply take a stem cutting from a healthy plant and replant it in the substrate. Roots typically develop within 2-4 weeks .

• Pruning: Regular pruning (every 4-6 weeks) by cutting the tops of stems encourages the plant to bush out, creating a fuller appearance .