Cleome spinosa Seeds | Spider Flower
LATIN NAME: Cleome spinosa
COMMON NAME: Spider Flower
Plant Profile
The prickles that give the old specific epithet spinosa its meaning are not on the stem. They are stipular spines, a pair of hardened, downward-curving thorns formed from the stipules at the base of each leaf stalk, and they sit along the whole length of the plant. Handle a mature row without gloves and the scratches will tell you where they are. Some selections have been chosen for weaker spines, and the modern sterile hybrids are close to thornless.
The plant is a fast-growing annual or short-lived perennial with a woody base and a strong taproot. Its leaves are palmately divided into five to seven leaflets carried on a long stalk, and the whole plant gives off a pungent, resinous smell when bruised. The flowers are borne in a loose raceme that opens from the bottom upward, so a plant in full flower carries buds at the top, open blooms in the middle and thin green seed pods below. The pods are long, narrow capsules that split from the base upward when ripe and scatter a fine black seed, and a border that has carried spider flowers for a season will usually produce its own seedlings afterwards.
Garden forms have been selected for decades. The older series, distinguished by names such as ‘Helen Campbell’ for the white form and ‘Rose Queen’ and ‘Violet Queen’ for the pink and purple ones, all grow to about a metre and a half and all set seed freely. Newer hybrids such as ‘Senorita Rosalita’ are sterile and almost thornless, which keeps them compact and stops them seeding into the border; they flower for as long as the older sorts and need no deadheading. Growers who want to save seed should keep to the open-pollinated series, because the sterile hybrids produce none, and the open sorts will cross with each other in a mixed row.
Science & Biotechnology
This species was chosen as a reference genome for its family, and the reason is taxonomic rather than horticultural. Cleomaceae sits next to the cabbage family, and the two lineages share an ancestor, so comparing the spider flower genome with that of Arabidopsis has been used to trace how chromosome number and flower structure were rearranged as the cabbages diversified. The work placed the species in a small genus of its own and gave breeders a map of the genes behind flower form.
The order to which this plant belongs makes glucosinolates, the compounds that give mustard and horseradish their bite, and the spider flower carries the same pathway in its leaves and seed, at lower concentration than a cabbage. Break a leaf and the pungent note is that chemistry at work, together with a set of terpenes in the leaf oil. The flower colour itself comes from anthocyanins, and the pink and purple selections differ chiefly in how much of the pigment is laid down in the petal tissue. The seed also contains a fixed oil that has been examined as a possible industrial feedstock, since the plant sets a heavy crop of seed in a single season.
Uses & Benefits
Look at a spider flower from the side and the oddity becomes obvious: the petals and the six long stamens sit at the end of a green stalk that lifts them clear of the leaves and the stem. That stalk is an androgynophore, an elongated internode that carries both the stamens and the ovary at its tip, and it is the structural fact that identifies the genus however the flowers are coloured. It gives the bloom its insect-like look, with the stalk as a green body and the stamens as legs reaching outward, and it is also why the plant can be pollinated by moths and bees that approach from any direction.
Growing from Seed
The taproot is the reason this plant should be sown where it is to flower. A seedling moved from a tray stalls, forks its root and often never recovers, so mark the site, work the soil to a fine tilth and sow thinly on the surface, pressing the seed in and covering it with no more than two millimetres of soil, because light helps the seed to come up. Water the drill with a fine rose and keep the ground damp until the seedlings are through, then thin them in stages, first to five centimetres and finally to forty-five centimetres apart, keeping the strongest plant at each station. Shortly after the final thinning, water in a balanced liquid feed at half strength.
Established plants are surprisingly drought-tolerant for a plant with soft stems, but a dry spell in the middle of summer will shorten the flowering period, so water deeply rather than lightly. Tall selections benefit from a single cane or a loop of twine kept low around the row, because the stems are brittle at the base and a summer storm will snap them. Deadhead a few stems to keep the display going, or leave the pods to ripen for seed if the self-sown seedlings are welcome. Spider flowers have few pests; flea beetles and aphids can mark young growth, and damping off kills seedlings where the soil is cold and wet, so do not sow into ground that has not warmed. The plant resents being crowded, and a thick row in still air invites powdery mildew on the lower leaves.
Our Take
Sow it once and it will usually find a place for itself in the border thereafter. Growers who want the same airy height behind it should add Cosmos bipinnatus, which takes the same direct sowing and the same thin soil, or the tall purple stems of Verbena bonariensis, which let the spider flower show through them. For scent in the evening, plant Nicotiana sanderae along the same row, since it opens its flowers as the spider flower’s pods begin to form.
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