Drosera rotundifolia

Round Leaf Sundew

 Drosera rotundifolia, Round Leaf Sundew; photo courtesy of David H. Firmage
Round Leaf Sundew
Photo courtesy David H. Firmage

Flora, fauna, earth, and sky...
The natural history of the northwoods

Name:
  • Drosera, from the Greek, droseros (droseros), "dewy, watery"
  • rotundifolia, from the Latin, rotundus, "round, spherical" and folius, "leaf"; hence "round leaf"
  • Common Name, from the shape of the leaf
  • Other common names include: Common Sundew, Dew Plant, Red Rot, Round-leaved Sundew, herba rosellae, Youthwort, hierba de la gota, hierba del rocío (Castellano), herba de la gota, resplendor de la nit (Catalán), rundbladet soldug (Dan), Ümaralehine huulhein, huulerohi, mokahein, kõrvalusikas, putukasööja, ohatserohu, silmarohi (Est), pyöreälehtikihokki (Fin), droséra, rossolis à feuilles rondes, rosée du soleil, drosère, rossolis, herbe à la rosée (Fr), Lus na Feàrnaich, Ròs an t-Solais (Gaelic), sonnenthau rosollis, rundblättriger sonnentau (Ger), kereklevelû harmatfû (Hun), sóldögg (Is), rosolida (It), rundsoldogg (Nor), rorela, orvalhinha, rorella (Por), rocio del sol (Sp), rosièka okruholistá (Slovak), rundsileshår, sileshår, daggört (Swe)

Taxonomy:
  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Dilleniidae
        • Order Nepenthales
          • Family Droseraceae, the Sundews
            • Genus Drosera, the Sundews
  • Taxonomic Serial Number: 22017
  • Also known as Drosera longifolia

Description:
  • An insectivorous, short-lived herbaceous perennial of open bogs.
  • Leaves a basal rosette. Blades round, depressed, and lying flat on ground; ¼"-½" long and as wide or wider. Upper surface of blades covered with reddish, glandular hairs tipped with a sticky, glutinous secretion resembling a dewdrop that traps insects, hence its name. Petioles ¾"-2" long and covered with sticky hairs.
  • Roots usually shallow (less than 2½"), consisting of a taproot, functional for less than a year, replaced by mostly horizontal adventitious roots with a few root hairs.
  • Flower structure a one-sided raceme, with 2-15 flowers on a 2"-10" long stalk . There may be one to seven racemes per rosette.flowers which only open in the sunshine. Flower-stems erect, slender, 2 to 6" high, at first coiled inward bearing a simple raceme, which straightens out as flowers expand; these are very small and white, appearing in summer and early autumn.
    • Sepals 5, 4mm-5mm
    • Petals 5, white to pink; longer than sepals
    • Stamens 5; shorter than petals
    • Pistils of 3 styles
  • Fruit a capsule with numerous small seeds.
  • Seed tiny, light brown, and shiny, with fine lines; only about 1mm long.
  • Compensates for the low available nutrients in its habitat by catching and digesting insects. Insects are caught with the sticky glandular leaf hairs, the leaf then folding around the prey. The hairs secrete proteolytic enzymes which digest the insect and enable the plant to absorb nutrients through its leaves. Insect capture is generally believed to enhance growth and reproduction. It is significantly correlated with total leaf number, number of new leaves formed, and total leaf area. The benefits of insectivory may be site dependent; sundew may benefit most from insect capture on the most nutrient-poor sites.
  • This secretion is most abundant when the sun is at its height. These hairs are very sensitive, they curve inward slowly and catch any insects which alight on them; the fluid on the points also retains them. After an insect has been caught, the glandular heads secrete a digestive fluid which dissolves all that can be absorbed from the insect. It has been noted that secretion does not take place when inorganic substances are imprisoned.

Identification:
  • Unmistakable as a Sundew; nothing else like it in the North Country.
  • Distinguished from the other North Country Sundew, the Spatula Leaf Sundew (Drosera intermedia) by the round, rather than oblong, leaf.

Distribution:
  • Greenland and Newfoundland to Alaska, south along the Pacific coast to California and inland to Montana and Colorado; in the East, from Nova Scotia south to Florida, west to the Mississippi River, and Minnesota.
  • Also Europe, Asia, South Africa, and South America.

Habitat:
  • Most often bogs, but also swamps, rotting logs, mossy crevices in rocks, or damp sand along stream, lake, or pond margins. Generally associated with sphagnum mosses, growing on floating sphagnum mats or hummocks. May also grow on other moss or sedge peat soils.
  • Usually sites with a high water table or high precipitation and humidity. It requires continually moist or wet situations generally with the water table 1"-16" below the soil surface. Flooding can be tolerated for several weeks, but dry periods for but a very short time.
  • Grows in organic acid soils low in available nutrients (nitrogen and phosphorous, and calcium). Not found on limestone soils; high calcium concentrations may be toxic to the plant. Reported from sites ranging from neutral pH (7.3) to very acidic (3.2) Acidic soils with low nutrient concentrations (nitrogen, phosphorous, or calcium) seem to be the most common substrate.
  • Very shade intolerant. Because it is so small, even sedges, grasses, and small shrubs may limit light. Shaded plants may not develop a rosette but instead have a more spindly habit.
  • Adaptation to nutrient-poor conditions allows it to be very competitive and persistent in acid wetlands. It has invaded disturbed sites in bogs after peat mining, ditching, and burning. However, easily shaded out if succession leads to the invasion of bogs by woody vegetation.
  • Grows throughout Europe on wet heaths, moors, and sphagnum bogs, especially in Wales.
  • Frequent fire is necessary to maintain bog habitats. Fire suppression has led to the invasion of woody species from the surrounding forest. Frequent surface fires remove the young woody plants advancing from bog edges. Where woody vegetation is dense and has lowered the water table, fires can be severe and may alter the subsequent composition of the vegetation.
  • Most likely killed even by fast moving, low-severity fires. However, fires in bogs are generally patchy and sundew probably survives in unburned microsites. Colonizes recently burned peat surfaces.

Associates:

History:
  • Leaves can curdle milk and were used in Sweden to make cheese.
  • Fresh leaves have also been used to treat warts.
  • Has been used as a remedy for respiratory ailments.
  • Early herbalists believed that the 'dew' on the sundew leaves, which persisted even in the hottest sun (hence the name!) possessed the property to endow longevity and youthfulness to those who drank it.

Uses:
  • Sundews (Drosera spp.) generally survive better than other carnivorous plants and can naturally invade disturbed bog sites where other vegetation has been removed, such as after roadside ditching or burning.
  • Contains an antibiotic effective against Streptococcus, Staphylococcus, and Pneumococcus bacteria.
  • Clearing and drainage of peat bogs or swamps for peat mining, millpond construction, access to timber, and agricultural purposes have resulted in the decline of habitat by altering site conditions in many areas. Drainage also has an indirect negative effect by diminishing the numbers of prey that have aquatic larval stages.
  • Insectivorous plants may add to the nutrient pool on the nutrient-deficient sites where they most often grow.

Reproduction:
  • Reproduces vegetatively or by seed.
  • Vegetative reproduction takes place when leaf buds form plantlets, or when axillary buds below the rosette form a secondary rosette. As the stem decays, the two separate.
  • Cross pollinated by wind or insects when flowers are open during the day; self-pollination may take place as flowers close in the evening.
  • Fruits often persist unopened, and seeds are released when the fruit rots. The fusiform seeds are 0.06"-0.07" (1.5-1.8 mm) long and 0.008" (0.2 mm) wide and have an inflated testa. Air trapped in the testa makes the seed buoyant and capable of floating for days on water surfaces. Seeds may be carried some distance with snowmelt and flooding.
  • Plants flower in their first summer and every year thereafter, generally from June to September. Flowers open one per day, starting from the bottom of the inflorescence. Seed dispersal begins in July and most seeds fall before winter.

Propagation:
  • By seed, following cold stratification.
  • Root division most successful method

Cultivation:
  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Cultural Requirements
    • Sun full
    • Soil moist, very acidic, rich in peat moss or sphagnum moss, with a pH of 4.0 to 5.0.
    • Water
    • Fertilization not recommended. Sundew does not respond positively to fertilization and burns easily.
  • In a bog garden, spreads rapidly to form a natural carpet.
  • Set nursery plants so they rest just on the surface of the ground; the roots will reach down for the moisture they need. Propagate additional plants by root division or from seeds. To guarantee sufficient moisture for seedlings, plant the seeds in a pot that is set into a dish kept filled with water. Osmosis will keep the surface soil damp. Given a nearly natural environment, will also reproduce itself readily from seed.
  • Available by mail order from specialty suppliers.

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Last updated on 26 February, 2004