Native Plants of Hawai‘i

Bidens torta

Asteraceae or Sunflower family [Five-minute families]

Synonyms: Bidens fulvescens, Bidens fulvescens f. indivisa, Bidens micrantha var. kaalana, Bidens personans, Bidens waianensis, Campylotheca micrantha f. dissecta

Koʻokoʻolau

Kokolau, Kōʻokoʻolau, Koʻolau

Corkscrew beggarticks

Natural Range & Environment

Bidens torta is endemic to O‘ahu and is present in both the Wai‘anae Mountain Range and the northwestern part of the Ko‘olau Mountain Range from 300 to 1,200 m (984 to 3,937 ft). It is an adaptable and often common species with a wide range of habitats from dry ridges all the way to wet forests, even being found in bogs [Wagner et al. 1990].

The daisy-like flowers of Bidens torta look much like those of the many other endemic species of koʻokoʻolau. What sets this species apart is its curious corkscrew-like achenes (fruits) (photograph of developing achenes courtesy of Joel Lau ©; photograph of mature achenes courtesy of Hubert Szczygieł CC BY-NC 4.0).

While all Bidens torta have compound leaves, both the size of the leaves and how lobed the leaflets are can vary dramatically between individual plants. Here are just two extremes: a large leaf without lobes (photograph courtesy of Joel Lau ©); small leaves with lobing (photograph courtesy of Kellen Apuna CC BY-NC 4.0). In the wild, a blooming B. torta can be an amazing sight (photograph courtesy of kairigney CC BY-NC 4.0). Meanwhile, cultivated B. torta survive but often struggle as they endure frequent pest and disease infestations.

Description

Bidens torta is a medium-sized (up to about six feet [2 m] in height) short-lived perennial herb that can become slightly woody at its base and on its older branches. Cultivated plants may not live longer than a year.

While the leaves of Bidens torta are always compound (leaves with leaflets), their size and shape can vary dramatically between plants (see above photographs for two extremes; see Plants of Hawai‘i herbarium collection for other examples). While not always, the leaflets usually have serrated margins and may be covered with hairs when young.

Bidens torta produces multi-branched clusters of daisy-like flower heads that can have inner florets that are either perfect (bisexual) or are all pistillate (female), in which case the entire plant is female. This breeding system is thought to maximize viable seed production in wild populations since female plants do not need to divert energy and resources to producing pollen [Ganders & Nagata 1984]. However, this dichotomy can complicate seed collection from cultivated plants (see Growth Requirements below).

Pollinated perfect or female florets develop into black (when ripe), irregularly twisted achenes (single-seeded fruits) that in their extreme look like tiny corkscrews, hence the common non-Hawaiian name, Corkscrew beggarticks (see photographs above). Achenes are wingless and usually lack awns (projections at the end of the achene) [Seeds of Hawaii].

Growth Requirements

General

Bidens torta would not be my (Koebele) first choice for a ko‘oko‘olau to add to a landscape. It is more prone to pest and disease problems than some other ko‘oko‘olau species such as B. amplectens and B. hawaiensis. However, in my opinion, its unusual corkscrew-like achenes make it a curiosity worth the extra care it requires. To make that care (e.g., frequent spraying with insecticide) a bit easier, consider keeping your B. torta in a pot rather than planting it in the ground.

Place your Bidens torta in the coolest but also the sunniest place available. Also, select a location with a consistent (but not strong) breeze. Combined, these will help prevent infections of powdery mildew. While wild plants are sometimes found in relatively dry sites, avoid any type of water stress with your cultivated ko‘oko‘olau; always keep the soil or media surrounding its roots moist but also make certain the soil or media drains away excess water easily. I have only grown ko‘oko‘olau in rocky clay-dominant soil or a media mix of sphagnum peat moss, vermiculite, and black cinders or perlite (approximately one-third of each medium). However, I suspect it would also grow well in more organic-dominant or cinder-dominant soils or media mixes. Of course, if you are growing a ko‘oko‘olau that originated from a bog plant (not recommended), then all the above water, soil, and media recommendations should likely be “tossed out the window.”

Cultivated ko‘oko‘olau grow fast but typically do not live very long. You can expect your planted Bidens torta to be about two feet (61 cm) or more tall and flowering in a year or less. Containerized ko‘oko‘olau usually become stunted unless progressively transferred to larger and larger pots. I have never had my in-the-ground ko‘oko‘olau live past two years or my potted ko‘oko‘olau past three. And I never fertilized my planted ko‘oko‘olau; my potted ko‘oko‘olau received an application of granular controlled-release fertilizer every six months.

Because cultivated ko‘oko‘olau are typically short-lived, you will need to replace them every one to three years if you wish to keep them long-term. The easiest way to do this is by rooting cuttings of your existing plant. However, propagating ko‘oko‘olau from cuttings doesn't entirely "set back the clock" on these short-lived perennials, and these cloned plants often lack the vigor of ko‘oko‘olau propagated from seeds. Also, unlike seeds, you cannot easily store away a hundred ko‘oko‘olau clones in your refrigerator.

Propagating ko‘oko‘olau from seed comes with its own set of problems. First is the unusual breeding system of Hawaiian Bidens described above (see Description above). In order to get viable seed, you need to make sure your plant is producing perfect (bisexual) florets and not just pistillate (female) florets. This requires close examination of the flower head. Or perhaps an easier means is to just maintain several flowering B. torta at the same time, increasing the odds that at least one of the plants has perfect florets.

The second problem is Bidens torta can successfully hybridize with other native Bidens species [Ganders & Nagata 1984; Plants of Hawai‘i]. This makes collecting seeds of known genetic identity a challenge. Fortunately, a study by Knope et al. [2013] showed that B. torta cannot be successfully pollinated by the introduced, naturalized, and common B. pilosa and B. alba. Unfortunately, Knope et al. [2013] did not test the other two introduced and naturalized Bidens species, B. cynapiifolia (found on all the main Hawaiian Islands except Ni‘ihau and Kaho‘olawe) and B. gardneri (currently found on Moloka‘i) [Flora of the Hawaiian Islands]. Therefore, before your ko‘oko‘olau dies, you need to decide if you are a purist and want to ensure the genetic identity of any seeds you collect or if you are okay with the possibility that the seeds you collect will have hybrid genetics (most likely native x native; much less likely alien x native). Of course, if you are only growing B. torta and there are no other native or alien Bidens in your landscape or nearby —honeybees typically fly one to two miles from their hive —the chances that your B. torta is producing genetically-pure seeds are more likely. However, the only way to be absolutely sure about the genetics is to bag any young flower heads you plan to collect achenes from before they open and then pollinate them by hand. Past research [Ganders & Nagata 1984] has shown that hand-pollinating between flowers results in more viable seeds than hand-pollinating within flowers (i.e., self-pollination). Refer to Pritchardia martii for other details on how to collect genetically-certain seeds.

Pests and Diseases

Ko‘oko‘olau in general, and Bidens torta in particular, are frequently attacked by spider mites (most common), aphids, scale insects, and spittlebugs. Snails and slugs can also sometimes become a problem. Ko‘oko‘olau are also prone to powdery mildew infections; look for white patches on the leaves. Refer to the Pests & Diseases page for methods to control all the above-mentioned pests and diseases.

Uses

Ancient Hawaiian

Nearly all the native Hawaiian Bidens species have the collective names Kokolau, Koʻokoʻolau, Kōʻokoʻolau, and Koʻolau. Therefore, it is (currently) impossible to know if all the species (about 20) were used, or were used in the same way(s) by pre-contact Hawaiians. Below are the ancient uses we have found in the credible literature for plants with the names listed above.

Leaves, both fresh and dry, were used medicinally. Krauss [2001] has the most extensive account, stating that native Bidens and then later the introduced kī nehe (Bidens pilosa) were used sometimes alone and sometimes mixed with other plant ingredients to make a tea for the treatment of ʻea (thrush), constipation, asthma, tuberculosis (a post-contact disease), and as a generalized tonic.

Ka‘aiakamanu & Chun [2003] add stomach problems, "feminine illnesses," swollen neck or cheeks, and "splitting headache" to the list of treated ailments.

Modern

Today, fresh and dried koʻokoʻolau leaves are still brewed and drunk as a medicinal tonic or as an alternative to other commercially available teas. Abbott [1992] has stated, "I find that the roughly half a dozen species common in Hawaiʻi offer two or three slightly different flavors, each a bit more subtle than commercial black tea." Koʻokoʻolau tea, along with other Hawaiian teas, is sold by a few small commercial exporters, primarily using koʻokoʻolau grown on Hawai‘i Island.

Koʻokoʻolau flowers are occasionally used in lei [McDonald & Weissich 2003].

Special Features and Information

General

Asteraceae is a very large family of mostly herbaceous plants with about 32,000 species within 1,900 genera with a subpolar to tropical worldwide distribution. Nearly all Asteraceae have what appears to be a single daisy-type flower that is actually a composite of several to many much smaller flowers called florets [WikipediA:Asteraceae]. There are about 250 native and non-native Asteraceae in Hawai‘i, with a little more than half being native [Flora of the Hawaiian Islands].

Many of the endemic Hawaiian Bidens species, including B. torta, have adopted an unusual breeding strategy (see Description above) [Wagner et al. 1990]. Additionally, many have abandoned the method of seed dispersal most common among their non-native congenerics. Most non-native Bidens, like the introduced, naturalized, and now common B. pilosa (Spanish needle), have harpoon-like awns (horn-like projections) on one end of their achenes (single-seeded fruits) that firmly attach to bird feathers, mammal fur, and people’s socks, thereby aiding in the long-distance dispersal of their seeds [WikipediA;Bidens; Britannica]. In contrast, many Hawaiian Bidens have no awns at all, or the awns are reduced or without the harpoon-like barbs. Instead, some ko‘oko‘olau have winged achenes, thought to help with dispersal by the wind. Others have corkscrew or irregularly twisted achenes, where it's anyone's guess why they have assumed these shapes (see photograph below). However, generally, botanists think that these alternatives to harpoon-like awns are a way for the Hawaiian species to limit, not extend, their seed dispersal [Carlquist 1980].

Pollination studies have demonstrated that native Hawaiian Bidens species will produce vigorous hybrids when crossed with other native Hawaiian Bidens species [Ganders & Nagata 1984]. Additionally, natural hybrids between Bidens torta and B. amplectens have been observed in the Wai‘anae Mountain Range, O‘ahu [ECOS].

A comparison of one non-native (far left) and three native Hawaiian Bidens achenes, including B. torta (photograph courtesy of G.D. Carr ©).

Bidens torta has relatively modest flowers compared to some of the other native Hawaiian Bidens species (photograph courtesy Ganders & Lamoureux via G.D. Carr ©).

Hawaiian Name

Bidens cosmoides is the only native Hawaiian Bidens with the species-specific Hawaiian name Po‘olā nui, while the genus is collectively referred to as Koʻokoʻolau or Koʻolau, with Kōʻokoʻolau being a variant spelling [Wagner et al. 1990; Pukui & Elbert 1986]. According to Andrews [1922], Kokolau is another name for Koʻokoʻolau. Koʻokoʻolau, Koʻolau, Kōʻokoʻolau, and Kokolau may all be compound Hawaiian words. However, because their component syllables (e.g., Koʻokoʻo, Lau) have many disparate meanings, it is impossible for us to determine an underlying meaning for the names.

Etymology

Bidens is derived from the Latin bi, meaning "two," and dens, meaning "tooth" or "teeth," referring to the two awns on the achenes (fruits) [Wagner et al. 1990]. The species name, torta, is the feminine form of the Latin word tortus, meaning "tortuous, turned, twisted, crooked," referring to the twisted or coiled achenes of this species [Mobot; A Grammatical Dictionary of Botanical Latin]. The non-Hawaiian name for Bidens torta is Corkscrew beggarticks.

BPK