Ludwigia octovalvis (Jacq.) P.H. Raven
Mexican primrosewillow, primrose willow, Mexican primrose-willow
Mexican primrose-willow is native to, or naturalized in, North, Central, and South America, Europe, Australia, Southeast Asia, the Middle East, and central West Africa. It spreads quite vigorously and is considered invasive in some habitats.
Plants: Herbaceous plants are erect and multiply branched. They may develop woody bases, with red-brown stems, and reach 13′ (4 m) in height.
Leaves: Alternate, lanceolate to ovate, with narrow tips and bases. Leaves are gray-green due to long, pale, appressed hairs, and have a reddish to pale midrib. As they age, they may turn red. They are ⅜–6″ long ⨉ ⅛–1½″ wide (1–15 cm ⨉ 4–40 mm).
Flowers: Solitary yellow flowers appear in leaf axils or at branch tips. Each flower has four obovate or narrowly obovate sepals, four petals ⅜–¾″ (1–2 cm) long, and 8 stamens. The stigma is round, shiny, and sticky, “sitting in the end of the style like an egg in an egg cup.” Flowers appear from July to October.
Fruits: Capsules are ¾–1¾″ (2–4.5 cm) long, splitting into eight sections when mature. Seeds are tiny, about ~1/32 ⨉ ~1/32″ (0.6–0.8 ⨉ 0.5–0.7 mm).
Habitats: Swamps or wetlands, with moist or shallowly submerged soils: damp grasslands, rice fields, ditches, lakes and pools, drains, sandy or silty floodbanks, gravelly riverbeds, etc.
Online References:
4/14/2015 · Everglades National Park, Florida · ≈ 9 × 8″ (24 × 21 cm) 
4/11/2015 · Loop Road, Big Cypress National Preserve, Florida · ≈ 8 × 6″ (19 × 16 cm) 
4/11/2015 · Loop Road, Big Cypress National Preserve, Florida · ≈ 10 × 7″ (25 × 16 cm) 
4/15/2015 · Florida · ≈ 11 × 7″ (27 × 18 cm) 
4/11/2015 · Loop Road, Big Cypress National Preserve, Florida · ≈ 6 × 4½″ (16 × 11 cm) 
4/11/2015 · Loop Road, Big Cypress National Preserve, Florida · ≈ 10 × 7″ (25 × 16 cm) 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| Subkingdom | Tracheobionta | Vascular plants—plants with a “circulatory system” for delivering water and nutrients |
| Division | Magnoliophyta | Flowering plants, also known as angiosperms |
| Class | Magnoliopsida | Dicotyledons—plants with two initial seed leaves |
| Subclass | Rosidae | Roses, legumes, proteas, dogwoods, hydrangeas, mistletoes, euphorbias, grapes, many more |
| Order | Myrtales | Includes myrtles, leadwoods, loosestrifes, pomegranates, evening primroses, many others |
| Family | Onagraceae | Willowherb/evening primrose family |
| Genus | Ludwigia | Named for Christian Gottlieb Ludwig (1709-1773), German botanist, plant collector and a professor of medicine in Leipzig |
| Species | octovalvis | Eight-valved, referring to the 8-valued fruit capsules |
Ludwigia octovalvis description by Thomas H. Kent, not updated.
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