Drosera binata

A leaf that keeps dividing

The leaves of Drosera binata stand on long, wiry stalks and split at the top into narrow, sticky arms. The New South Wales flora gives the stalks as 4 to 30 cm long and the arms as 2 to 10 cm, usually forked once and sometimes more often. White flowers about 25 mm across open in spring and summer, 15 to 30 to a branched stalk that can reach 50 cm ^[5]. Each new leaf unrolls from a tight coil like a fern frond, and each division unrolls the same way, which protects the tips until the leaf is mature ^[2]. Seedlings start with unforked leaves ^[4].

How many times a leaf divides is the main difference between the forms growers trade. Writing in Carnivorous Plant Newsletter in 1984, I. Gilbert described them this way ^[2]:

WCVP does not accept these varieties and lists D. binata var. dichotoma and var. multifida as synonyms of D. binata ^[1]. ICPS notes that the single-forked plants are the most widespread, that multi-forked forms are restricted to eastern Australia north of Sydney, and that forms from cooler places tend to be smaller ^[4].

Swamps, cliffs and burnt bogs

ICPS describes the species as mainly a plant of sandy marshes ^[4]. In New South Wales it grows in wet sand and sandy peat in swamps, on creek banks and on seepage lines in rock faces ^[5]. Ivan Snyder, writing about a 1991 hike in the Blue Mountains, found it rooted in crevices of vertical sandstone cliffs where water seeped down the rock. The largest plants hung over pools below waterfalls, and plants in shade had weaker, drooping leaves than those in sun ^[9]. In New Zealand it ranges from the coast to subalpine bogs, also grows in poorly drained acid pasture, and is often abundant after fires ^[3].

The plant was first collected on Australia’s south coast by the French expedition under d’Entrecasteaux in 1792 and was described by the expedition’s naturalist, Labillardière. Gilbert gives 1808 as the year of the description ^[2], while WCVP dates the published name to 1805 ^[1].

IUCN has assessed it for the Red List; see its Red List assessment ^[6]. New Zealand’s 2023 national assessment lists it as Not Threatened ^[3]. Regional assessments are less reassuring: it is listed as declining in Northland and Auckland, vulnerable in the Wellington region and endangered in Otago ^[3].

The dormancy that catches growers out

ICPS says this species can be awkward if you forget where it comes from. All forms go dormant: they stop producing leaves and die back to the ground. Under natural light this happens with the seasons, while under lights it happens now and then ^[4]. Gilbert describes a gradient in the wild. Plants in the north of the range have one or more short dormant periods in the cooler months, and southern plants go dormant in autumn and do not reappear until mid-spring ^[2]. ICPS notes that most varieties look dead while dormant until you inspect the growth bud ^[4].

For the temperate forms, ICPS recommends growing them outdoors. Typical Tasmanian and New Zealand plants can stay out all year in USDA zone 9 and warmer, some forms take colder weather under a good mulch, and anywhere the soil might freeze the pots should spend winter in a garage or other cool, protected place ^[4]. Two New Zealand locality forms show the range ^[4]:

• Coromandel: a lowland form with leaves 10 to 20 cm tall that turns dark red in full sun and expects a short, mild winter.
• Waihohonu, Desert Road (1080 m): a highland form with leaves 6 to 10 cm tall that stays dormant longer and can survive USDA zone 7 winters outdoors if protected from freeze-drying.

A grower writing for ICPS also lists the D. binata complex among plants that succeeded outdoors year round in a Pacific Northwest bog garden ^[10]. The dormancy guide and bog garden guide cover winter handling.

Pots, soil, light and water

ICPS calls the species not very picky about soil: standard 1:1 peat:sand works, and 1:2 peat:sand in the top half of the pot is better. The guide says the plants like large pots, and notes that in nature some forms send long, rope-like roots down to tap water under the sand; elsewhere the same guide suggests small pots in trays of water for adult plants ^[4]. Gilbert recommended broad, shallow pots to hold the large root system ^[2]. On water there is no disagreement: ICPS stands the pots in trays of water ^[4], and Gilbert kept the mix wet to sodden in growth and slightly moist in dormancy ^[2].

Light matters for the dew. Gilbert warned that in poor light growth is weak and mucilage is not produced ^[2], and ICPS puts most Drosera at 15,000 to 25,000 lux under lamps ^[8]. ICPS notes that its Tasmanian form grows about 10 cm tall under artificial light ^[4]. See light for carnivorous plants.

Seed is harder than it looks

Most D. binata in cultivation are sterile, self-incompatible or otherwise do not self-pollinate. Self-incompatible plants need pollen from a second, unrelated plant of the same type, which is hard to find because the common forms circulate as clones. When flowers last two days, today’s flowers may need pollen from yesterday’s ^[4]. As far as the ICPS author knows, the self-fertile forms come only from New Zealand; the Coromandel form self-pollinates, while the Tasmanian form pictured does not ^[4]. Some varieties grow for a year or two, set a lot of seed and die ^[4].

When seed is available, ICPS germinates it at 20 to 25 °C (70 to 80 °F) ^[4]. Gilbert wrote that it should germinate easily without cold treatment, and suggested two weeks in the refrigerator before sowing if it does not ^[2]. See sowing seeds.

Cuttings and named clones

Cuttings are faster than seed ^[4]. D. binata is one of the species that ICPS says can sprout quickly in the second month of a leaf cutting, with plantlets spaced only 1 or 2 mm apart along the leaf ^[11]. Root cuttings work too ^[4], and suckers can come up from any part of the thick, wiry roots ^[2]. The sundew leaf cuttings guide gives the method.

Three registered cultivars belong to this species ^[12]:

• ‘Giant’: wiry petioles up to 30 cm and leaves branching into 4 to 12 points, up to 60 cm across, with a brief winter dormancy.
• ‘Marston Dragon’: a 1983 seedling selection with pendulous stems up to 36 cm and wide segments dividing into two to eight points that curve like claws.
• ‘Ghost’: leaves and petioles that come up very pale green to white after dormancy, propagated by root cuttings and division.

The genus overview compares D. binata with the other sundew growing groups, including cold temperate species such as the round-leaved sundew.