Rhinotropis californica (California milkwort)

Rhinotropis spp.

Polygalaceae Western North America and Mexico

Native to North America

HardinessZones 7–10

Overview

Rhinotropis spp. is a genus of about 25 perennials and small shrubs in the family Polygalaceae, segregated from Polygala spp. and native mainly to western North America. Plants form low, often woody-based mounds or sprawling subshrubs 0.5-3 feet (15-90 cm) tall, with slender, branching stems and small, alternate, untoothed leaves 0.2-1.5 inch (0.5-4 cm) long. The flowers, borne singly or in short clusters, have an irregular form typical of the family: two petal-like wing sepals flank a tube of three petals, the lowest fringed or crested at the tip, in shades of pink, rose-purple, white, or greenish. Bloom comes mainly in spring and early summer, followed by small flattened capsules holding hairy seeds. Many species grow on dry, rocky or sandy ground and tolerate heat and drought once established. Growth is slow to moderate, and woody-based plants persist for several years. Foliage is sparse, and plants can look open or twiggy outside the bloom season. Some species are restricted to particular soils or habitats and are uncommon in the wild.

Native Range

Rhinotropis spp. occurs mainly in the western United States and Mexico, with a few species farther east, growing in chaparral, desert scrub, rocky slopes, pine and oak woodland, and sandy flats. Species such as Rhinotropis californica grow on dry slopes in California, while others are found on limestone, granite, or gypsum soils in the Southwest.

Suggested Uses

Grown in rock gardens, native and dryland plantings, and on dry banks and slopes, spaced 12-24 inches (30-60 cm) apart depending on species. The low, woody habit suits well-drained, sunny sites and naturalistic desert or chaparral gardens. Plants are less suited to rich borders or irrigated beds, where they tend to rot.

How to Identify

Recognized by small, irregular flowers with two petal-like wing sepals and a crested or fringed lower petal, carried on slender, branching, often woody-based stems with small untoothed leaves. Flower color ranges from pink and rose-purple to white or greenish. The crested lower petal and winged sepals separate Rhinotropis spp. from pea-family plants with similar shapes, and the woody base and western dry-habitat range distinguish many species from the mostly herbaceous Polygala spp..

Appearance

Size & Dimensions

Height6" - 3'

Width/Spread1' - 3'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~8 weeks

Spring Summer

Most species bloom in spring and early summer, generally March to June, with timing shifting later at higher elevations. Desert species flower after winter and spring rains, sometimes briefly. Individual plants bloom over several weeks, and a second flush can follow summer rain in some regions.

Detailed Descriptions

Flower Description

pink, rose-purple, white, or greenish

Foliage Description

green to gray-green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-10 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 Range6.0 - 8.0(Neutral)

357912

Soil Types

sand rocky loam

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

2-4 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Plants grow in full sun on lean, fast-draining sandy, rocky, or gravelly soils and need little water once established. They tolerate heat and drought but rot in rich, wet, or poorly drained ground. Many species resent transplanting because of deep or woody roots, so container-grown plants establish more reliably. Light trimming after bloom keeps the habit compact, though hard cutting into old wood may not resprout. Few pests trouble the plants. Cold tolerance varies by species, with montane forms hardier than desert ones.

Pruning

Trim lightly after flowering to keep the plant compact, removing spent flower stems and twiggy growth. Avoid cutting into bare old wood, which may not resprout. No routine pruning is needed for plant health.