Tread Lightly

Bristly mounds of tread lightly (Cardionema ramosissimum) look like scouring pads discarded along the edge of the trail. The white flowers are tiny (1/16 of an inch) and nestled deep within spiny foliage; unless you have excellent eyesight and get down on hands and knees, you will never notice them. This unfriendly looking plant is a cousin of carnation and sweet William.

The common name “tread lightly” appears to be a local name. The more common alternate names (“sandmat” and “sand carpet”) reflect its affinity to  sandy places, such as dunes. In the Reserve, tread lightly can be found in several areas along the trails in East and Central Basins, as well as in the dune area along Coast Highway.

Description ^2,3,4,89

Tread lightly is a low, compact perennial herb, usually less than 4 inches (10 cm) high and 12 inches (30 cm) wide. Numerous short, branching stems grow horizontally from a taproot. Branches are densely covered with leaves and stipules, giving them a bristly appearance. The leaves are green, often tipped with pink;  they are opposite, 1/2 inch (1.3 cm) or less in length, narrowly lanceolate in shape; they have smooth margins are smooth and end in a small spine.  A shorter, papery stipule is fused to the inner surface of each leaf base. Stipules are ovate to lanceolate and pointed or jagged at the ends. Dried leaves and stipules often remain in bands along the stem.

Tiny flowers about 1/8 inch (3mm) across are tucked among the leaves and stipules. Petals are not evident (they are reduced to tiny scales). There are five small sepals, which have long woolly hairs below and end in single small spines. The woolly sepals give the flowers their white color. There are 3-5 stamens, which alternate with sterile stamens. Anthers are heart-shaped. The pistil consists of one rounded, superior ovary with two short styles; the stigma is not differentiated and the style is receptive along its entire length. The major flowering time is April – June.¹

The fruit is a very small, one-chambered, one-seeded, bladderlike capsule with a papery wall. Unlike most capsules, it lacks a predictable line for splitting open. The sepals often remain attached to the developing fruit and they may drop from the plant as a unit before the fruit opens. This spiny unit may serve as a seed dispersal mechanism, catching a ride on feathers or fur of passing birds and mammals.²⁷¹

Classification ^2,11,44,143

Tread lightly is a dicot herb in the carnation, or pink, family (Caryophyllaceae). This is a family that occurs primarily in temperate climates. Members of this family have simple flowers carried singly or in loose clusters on jointed stems. Leaves are usually undivided. Flowers are bisexual and symmetrical, typically with five (or no) petals which are often notched at the ends, five (rarely four) sepals and five or ten stamens. The fruit is a one-chambered capsule.

The carnation family includes well known ornamental flowers such as carnations, pinks, bouncing bets, and baby’s breath. It also includes some well-known weeds such as the chickweeds.

in the Reserve, there are eleven species in the carnation family.⁴⁸ Most are low-growing and inconspicuous; the exception is the lovely southern pink (Silene laciniata), which has deep red flowers with “pinked” petals.

Ecology ²⁷⁰

In sand dune habitats, tread lightly is a preferred shelter for burrowing arthropods, and it has been postulated that it provides food as well as shelter.

Human Uses ⁴¹

Because of its dense mat formation, tread lightly has been recommended for erosion control on beaches.

We have found no records of use by local native Americans.

Interesting Facts ⁴

Tread lightly is thought to have originated in coastal South America. Most sources consider it to be native to California as well, assuming that the plant arrived here naturally (perhaps hitching a ride on the feet of migrating birds). However, it is also possible that it was brought here accidentally by early traders and travellers along the Pacific coast, in which case, its native status is in jeopardy.