Mimulus guttatus - Fisch. ex DC.

Seepspring monkeyflower grows best in full sun to partial shade and consistently moist or wet soils. It is particularly well adapted to streambanks, springs, seeps, pond margins, and shallow watercourses. The plant can tolerate saturated soils and may grow where water flows slowly across the ground. It is adaptable to sandy, loamy, and clay soils, provided sufficient moisture remains available. In cooler climates, plants can grow successfully in full sunlight. In hot climates, partial shade may help prevent excessive drying and heat stress. Seepspring monkeyflower is poorly suited to dry, exposed sites unless you provide irrigation. The Royal Horticultural Society recognizes its suitability for boggy conditions and full sun or partial shade. Habitat: Seepspring monkeyflower is native to western North America, from Alaska and western Canada south into northwestern Mexico. Its native distribution includes much of the western United States, extending eastward into parts of the Great Plains and Rocky Mountain region. Kew's Plants of the World Online recognizes a broad native range from Alaska to northwestern Mexico, including Chihuahua. The species grows in streams, springs, wet meadows, marshes, seepage areas, pond margins, and other wet habitats. It occurs from near sea level to middle mountain elevations, with local populations extending into higher elevations where suitable moisture is available. Seepspring monkeyflower has also been introduced to several countries outside North America, including parts of Europe, Australia, and New Zealand. In Australia, it has become naturalized in New South Wales, Victoria, and Tasmania, particularly around streams, drains, and other wet environments. USDA Hardiness Zones: USDA Zones 5–9 (approximate). Seepspring monkeyflower is relatively cold-tolerant and occurs across a broad range of elevations in western North America. It can survive freezing winters, particularly where its perennial root system is protected by moist soil. However, the species is variable, and some populations behave as annuals rather than persistent perennials. The proposed hardiness range is an estimate, not a verified species-wide classification. For cultivation, reliable moisture is generally more important than winter cold tolerance. Growth Rate: Fast under favorable conditions. Seepspring monkeyflower can develop rapidly in moist soils, producing numerous leaves, stems, and flowers during the growing season. Perennial plants can spread through rhizomes and by producing roots at stem nodes. This allows established populations to expand into surrounding wet ground. The species also produces numerous seeds, enabling new plants to establish where conditions are suitable. Moisture availability strongly influences its growth rate. Plants growing in continuously wet soil can be vigorous, while those experiencing drought may become stunted or die. Mature Size: Height: typically 15–65 cm (6–26 inches), occasionally reaching 80 cm (31 inches). Spread: Variable. Plants may develop creeping stems and rhizomes, allowing them to form colonies extending well beyond the width of an individual plant. A reliable maximum individual spread has not been established. Leaf length: Up to approximately 12.5 cm in the botanical description, although leaves are frequently smaller. Mature size varies considerably with growing conditions, elevation, and whether plants are annual or perennial. Cultivation: Seepspring monkeyflower is a useful ornamental plant for pond margins, bog gardens, streamside plantings, and consistently moist areas. Its bright yellow flowers provide color over an extended period, while the soft green foliage creates attractive ground-level vegetation. The species grows best in full sun or partial shade with continuously moist soil. It tolerates a range of soil textures, including clay, loam, and sand. In a garden, it can be grown beside a pond or in a container designed to retain moisture. Regular watering is essential during dry weather. The plant is particularly suited to locations where ordinary garden plants struggle because of persistent moisture. However, its ability to spread through seeds, rhizomes, and rooted stems means that cultivation should be carefully controlled outside its native range. In New Zealand, the species is naturalized and has been included in regional pest management measures. For edible cultivation, clean irrigation water is essential. Do not grow plants for food in drainage channels or ponds that receive contaminated runoff. Identification: Seepspring monkeyflower is a herbaceous plant with soft, often somewhat succulent stems and opposite leaves. It may behave as an annual or perennial, depending on the population and growing conditions. Stems: The stems are generally upright or ascending but may also spread along wet ground. They are often hollow and may develop roots at lower nodes. Some populations produce creeping rhizomes. The stems can be smooth or covered with fine hairs. Leaves: The leaves are simple and arranged oppositely. They are broadly oval to egg-shaped, sometimes approaching a rounded or kidney-shaped outline. The margins are irregularly toothed. Lower leaves usually have stalks, while upper leaves may be nearly stalkless and partly clasp the stem. The leaves are bright green, soft, and sometimes slightly fleshy. Flowers: The flowers are bright yellow with reddish or maroon spots on the lower lip and inside the throat. They are bilaterally symmetrical and divided into two lips. The corolla is tubular and widens toward the opening. The lower lip has two raised, often hairy ridges forming a prominent palate. This palate can partially close the flower opening. The calyx is tubular and has five unequal teeth, with the upper tooth noticeably larger than the others. The flower has four stamens and a single pistil with a two-lobed stigma. The flowers may occur individually in the leaf axils or in groups near the upper portions of the stems. Fruits and Seeds: The fruits are capsules containing numerous small seeds. The fruiting calyx often becomes inflated and partially closes around the developing capsule. The capsule eventually splits to release its seeds. Seed production can be abundant under favorable conditions. Roots: Perennial populations may develop rhizomes and roots at lower stem nodes. These structures allow the plants to persist and spread through wet habitats. The roots are not established as edible in the PFAF field notes. Similar Species: Roundleaf Monkeyflower (Erythranthe glabrata). Roundleaf monkeyflower, formerly Mimulus glabratus, is particularly similar to seepspring monkeyflower. Both species grow in wet habitats and produce yellow flowers with reddish markings. However, several characteristics help distinguish them. Roundleaf monkeyflower has nearly round leaves, while seepspring monkeyflower generally has egg-shaped leaves, sometimes with small basal lobes. The flower opening of roundleaf monkeyflower is not strongly closed by the palate, whereas seepspring monkeyflower has a more prominent palate that often partially closes the opening. Another useful distinction is the fruiting calyx, which does not fold inward in roundleaf monkeyflower but tends to close inward in seepspring monkeyflower. Both species commonly grow approximately 10–60 cm tall and favor streams, springs, and other wet habitats. The PFAF field notes describe the leaves of both species as edible, while the flowers of seepspring monkeyflower have a more clearly documented favorable taste assessment. Musk Monkeyflower (Erythranthe moschata) Musk monkeyflower is another moisture-loving perennial with yellow flowers. It differs from seepspring monkeyflower in its generally smaller flowers, sticky-hairy foliage, and characteristic musky scent. The New Zealand Plant Conservation Network identifies it as a similar species but notes that musk monkeyflower lacks the reddish blotches characteristic of seepspring monkeyflower. Its edible uses should not be assumed to be identical. Bigelow's Monkeyflower (Diplacus bigelovii): Bigelow's monkeyflower is a small annual wildflower of desert habitats. It produces conspicuous pinkish-purple flowers and generally grows in dry washes following seasonal rainfall. Its flowers are mild and delicate, but its edibility could not be verified. Consumption is therefore not recommended. Important Taxonomic Note: Seepspring monkeyflower was originally described as Mimulus guttatus DC. In 2012, the species was transferred to Erythranthe as part of a broader revision of the monkeyflower family. The accepted name is now Erythranthe guttata (DC.) G.L.Nesom. Kew's Plants of the World Online and the USDA Germplasm Resources Information Network recognize this name. The plant was historically classified in Scrophulariaceae but is now placed in Phrymaceae. Prefers rather moist places such as damp borders, margins of streams and boggy spots[1, 111]. Grows well in heavy clay soils. Thrives in full sun so long as the soil does not dry out[200], otherwise it is best grown in partial shade[187]. Grows well in shallow water, but it can be invasive[200]. Hardy to at least -20°c[187]. There is some confusion over the naming of this plant, the entry on edibility may refer to M. luteus, which is closely related to this species.