Penthorum spp.

Penthoraceae

Eastern North America and eastern Asia

Attracts Pollinators Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterHigh

HardinessZones 4–9

Overview

Penthorum spp. is a small genus of two wetland perennials, P. sedoides of eastern North America and P. chinense of eastern Asia, placed in its own family, Penthoraceae. Plants grow from creeping rhizomes in mud and shallow water, producing erect, branching stems 8-32 inches (20-80 cm) tall lined with narrow, lance-shaped, finely toothed leaves. In late summer and autumn the stems end in forked, one-sided cymes of small greenish-yellow flowers, each lacking petals or with petals quickly shed, arranged along curving branches that resemble the arms of a candelabra. The flowers mature into reddish, five- to seven-angled star-shaped capsules that persist and turn russet as the foliage takes on red tints in autumn. The genus grows in full sun to part shade in marshes, ditches, pond margins, wet meadows, and other saturated ground, tolerating standing water and periodic flooding. Despite the common name ditch stonecrop, the genus is not a succulent and is unrelated to true stonecrops. Plants spread by rhizome and seed to form patches in open wet habitats, and they die back to the rootstock over winter. The genus tolerates a wide pH range but needs constantly moist to wet soil.

Native Range

Penthorum spp. is native to eastern North America and eastern Asia, with P. sedoides ranging across the eastern and central United States into Canada and P. chinense found in China, Korea, Japan, and the Russian Far East. Plants grow in marshes, ditches, wet meadows, and along pond and stream margins.

Suggested Uses

Penthorum spp. is planted in rain gardens, bog gardens, pond and stream margins, and wetland restorations where soils stay wet. The red autumn capsules and foliage add late-season interest to naturalized damp plantings.

How to Identify

Look for erect, branching stems with narrow, finely toothed leaves in wet, open ground. In late summer the stems end in forked, one-sided sprays of small greenish-yellow, nearly petalless flowers along curving arms. These mature into reddish, star-shaped capsules that persist as the foliage reddens in autumn.

Appearance

Size & Dimensions

Height8" - 2'8"

Width/Spread1' - 2'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~6 weeks

Summer Fall

Flowering occurs in late summer and early autumn, roughly July through September. The small greenish-yellow flowers open along one-sided forked cymes and are followed by red, angled, star-shaped seed capsules. The capsules persist on the dried stems into winter.

Detailed Descriptions

Foliage Description

green, turning red in autumn

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

clay silt loam peat

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

1-2 years

Care & Maintenance

Care Guide

Penthorum spp. grows in full sun to part shade in constantly moist to wet, humus-rich soil and tolerates standing water and seasonal flooding. The genus suits marsh edges, rain gardens, bog plantings, and the shallow margins of ponds, and it declines if the soil dries out. Plants are cold-hardy through temperate winters and die back to creeping rhizomes each year. Spread is by rhizome and self-sown seed, so plantings widen over time in suitable wet ground. Few pests trouble the foliage. The genus adapts to a range of soil pH as long as moisture stays high.

Pruning

Cut spent stems to the ground in late autumn or late winter once the seed capsules have dried. The persistent reddish capsules can be left through winter for seasonal interest. Thin spreading rhizomes to contain the patch.