Drosera intermedia

Taxonomy

Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Caryophyllales
Family: Droseraceae
Genus: Drosera
Subgenus: Drosera subg. Drosera
Section: Drosera sect. Drosera
Species: Drosera intermedia Hayne, 1800

Droseraceae also holds the Venus flytrap (Dionaea) and the waterwheel plant (Aldrovanda) — three genera, three entirely different trap mechanisms, one family. The order Caryophyllales additionally contains the pitcher plants of the Old World tropics (Nepenthes), making it the order where carnivory has evolved most.

Common Names by Region

General / English: Spoonleaf sundew, oblong-leaved sundew, spatulate-leaved sundew, narrow-leaved sundew, water sundew
United Kingdom: Oblong-leaved sundew
Etymology: Drosera comes from the Greek droseros, dewy — a direct description of the glistening droplets on the leaves. Intermedia means intermediate, and what it is intermediate between has never been satisfactorily explained. Botanical references consistently note the reference as obscure. Hayne named it in 1800 and the reasoning did not survive.

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Description

Growth Habit

A small perennial forming a basal rosette, usually low and easily overlooked. Vigorous plants produce a short, elongated, leafy stem, lifting the rosette slightly above the moss surface — a habit that separates it from its close relatives and that is visible in this specimen.

Perennial, though reports on longevity conflict; growers describe it as short-lived even under good conditions, while wild colonies persist for years. In practice a bog population continues while individual plants turn over.

Size

Height: 5–20 cm (2–8 in), including the flower stalk
Rosette diameter: Typically 3–6 cm

Leaves

• Spatulate — spoon- or paddle-shaped, distinctly longer than wide, narrowing to a slender smooth stalk
• Blade roughly 3–5 mm wide by 6–20 mm long
• Held semi-erect rather than flat against the ground
• Upper surface densely covered with stalked glandular tentacles, each tipped with a clear droplet of mucilage
• Underside smooth and green, without glands
• Color runs green in shade to deep red or crimson in full sun — the red is anthocyanin, and a well-lit plant like the one here is fully colored

Flowers

• Five white petals, roughly 6 mm (¼ in) across — small, and easy to miss
• Borne in a one-sided raceme of 3 to 8 flowers, occasionally up to 20, on a long bare stalk
• The flower stalk arises from the side of the rosette, from below the crown rather than from the center. This is a reliable field character separating D. intermedia from roundleaf sundew, whose scape rises from the middle.
• Blooms late June through August
• Flowers open briefly, often for a single morning, and are largely self-pollinating

Fruit

• Small oval capsule, under 3 mm, splitting to release numerous dust-fine seeds

Quick ID

Spoon-shaped red leaves covered in glistening droplets, in sphagnum, with the flower stalk emerging from the side. Separates from roundleaf sundew (D. rotundifolia), which has circular blades held flat and a central scape, and from threadleaf sundew (D. filiformis), which has long linear leaves and pink flowers.

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The Trap

Field note

The droplets are the whole apparatus, and they are not dew.

Each tentacle is a stalked gland secreting mucilage — a viscous, sugary, enzyme-bearing solution. The sugar draws insects in. The viscosity holds them. A small fly landing on a leaf finds its feet stuck, struggles, and contacts more tentacles, which increases the adhesion.

Then the plant moves. Tentacles surrounding a captured insect bend inward toward it over minutes to hours, bringing more glands into contact and drawing the prey toward the center of the leaf. In many captures the leaf blade itself curls around the insect. This is slow motion — nothing snaps, and there are no trigger hairs. That is the Venus flytrap, a relative with a completely different mechanism, and the two get conflated constantly.

Digestive enzymes then break the insect down and the leaf absorbs the products directly.

Why any of this exists: sphagnum bogs are extremely nutrient-poor and acidic. Nitrogen in particular is scarce. Research on D. intermedia found the plants derive roughly half their nitrogen from captured insects. The carnivory is not a curiosity; it is how the plant makes a living in ground that cannot supply what roots normally provide.

Darwin worked on this genus extensively, publishing Insectivorous Plants in 1875 after years of experiments feeding sundews meat, glass, and various solutions to determine what triggered a response and what the plant could actually digest. It remains one of the more thorough pieces of botanical experimentation of the period.

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Known Range

Circumboreal through the northern hemisphere — Europe, Asia Minor, and northern North America — with an additional distribution down the Atlantic coastal plain and along the Gulf Coast, and disjunct occurrences at higher elevations in Cuba and northern South America.

In Pennsylvania, found in the eastern part of the state.

Western North American occurrences are sparse and isolated. In Idaho the species is known from only two entirely separate areas — the Selkirk Mountains in Boundary County and the Sawtooth Valley in Custer County — a pattern typical of a bog specialist stranded in refugia.

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Habitat

Classified as an obligate wetland species (OBL) — it does not occur outside continually wet ground.

• Sphagnum bogs, characteristically
• Fens, seeps, and shallow standing water
• Wet acidic sand among sedges
• Mossy margins of lakes, ponds, and ephemeral pools
• Full sun to light shade; the reddest and healthiest plants are in the open

On the sphagnum: the moss is not incidental. Sphagnum actively acidifies its surroundings, holds enormous quantities of water, and locks up nutrients as peat. It builds and maintains the conditions the sundew is adapted to. The two in this photograph are not simply neighbors — the moss is manufacturing the habitat.

Common associates include roundleaf sundew, cotton grass, cranberry, pitcher plants, and various bog sedges.

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Propagation / Cultivation

• Seed — surface sow on live sphagnum or peat, needs light, benefits from cold stratification
• Leaf cuttings root readily and are the standard method for growers
• Division of clumping plants
• Medium must be nutrient-free — pure sphagnum peat, or peat with sand or perlite. No potting soil, no compost, no fertilizer.
• Water with distilled water or rainwater only. Tap water carries dissolved minerals that kill these plants. This is the single most common cultivation failure.
• Never fertilize. The plant obtains its nutrients from insects, and root-zone nutrients damage it.
• Keep constantly moist — a tray of standing water underneath is standard
• Full sun produces the red coloration and the strongest plants
• Cold dormancy in winter is required for temperate forms

Suitable for bog gardens, troughs, and containers.

Never collect from the wild. Bog populations are fragile, slow to recover, and legally protected in many jurisdictions. Nursery-propagated plants are widely available and inexpensive.

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Threats and Conservation

• Habitat loss is the entire problem. Bogs and fens have been drained for agriculture and development, and cut for horticultural peat, across most of the range.
• Peat extraction removes the habitat and the substrate simultaneously.
• Succession — bogs left without hydrological maintenance fill in with shrubs and trees, shading out the low sun-dependent flora.
• Nutrient runoff from adjacent agriculture is quietly lethal. Adding nitrogen to a bog eliminates the advantage carnivorous plants hold and lets faster-growing competitors take over.
• ATV and foot damage to bog surfaces, which recover on a timescale of decades.
• Collection for the carnivorous plant trade.
• Listed as threatened, endangered, or of special concern in a number of U.S. states, with status varying widely by jurisdiction.

Peat bogs are also carbon stores of considerable size, and their destruction has consequences well beyond the plants living on them.

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Additional Notes

• Small, and worth kneeling for. A sundew colony is easy to walk past. The plants are a few centimeters across and read as red flecks in moss until you get down to eye level, at which point they become one of the more remarkable things in the eastern flora.
• Carnivory has evolved independently at least eleven times across flowering plants — sundews, pitcher plants of three unrelated lineages, bladderworts, butterworts, and others. It is a repeated solution to the same problem: how to grow where the soil holds no nitrogen.
• Historical medicinal use across Europe for coughs and respiratory complaints, with Drosera preparations appearing in herbals and still sold in some homeopathic contexts. Not a recommendation, and wild collection for this purpose has damaged European populations.
• A bog is an archive. Sphagnum peat preserves pollen, seeds, wood, and occasionally bodies, in anaerobic acidic conditions, for thousands of years. The ground under a sundew colony is a stratified record of everything that grew there since the glaciers left.

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Field Notes

• Look in July and August, when the flower stalks are up and the plants are easiest to locate.
• Look for red against green moss in open sunny sections of bog, not under shrubs.
• Stay on boardwalks and trails. Sphagnum compresses and does not spring back; a bootprint in a bog surface lasts years.
• Check the leaves for prey. A working sundew usually has several small insects on it, and the tentacle curl around a capture is visible with the naked eye.
• Photograph in side light. The mucilage droplets catch it and are what makes these plants photograph the way they do.

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