Bidens hawaiensis
Asteraceae or Sunflower family [Five-minute families]
Synonyms: Bidens hawaiensis var. conglutinata, Bidens skottsbergii, Bidens skottsbergii var. conglutinata, Bidens skottsbergii var. pololuensis, Campylotheca hawaiensis, Coreopsis hawaiensis
Koʻokoʻolau
Kokolau, Kōʻokoʻolau, Koʻolau
Hawai‘i beggarticks
Natural Range & Environment
Bidens hawaiensis is endemic to Hawai‘i Island and is found in the northwestern Kohala District, the eastern district of Puna, and around Kīlauea. It grows in open shrubland on old lava flows to more shaded mesic forests from 50 to 1,400 m (164 to 4,593 ft) [Wagner et al. 1990].
Bidens hawaiensis produces clusters of daisy-like flower heads about 2 inches (5 cm) in diameter (photograph courtesy of J.B. Friday ©). When pollinated, the perfect and female florets develop into black (when ripe), wingless, long, and straight achenes (single-seeded fruits) that have two awns (projections) without barbs at one end.
Both wild (photograph courtesy of J.B. Friday ©) and cultivated Bidens hawaiensis often grow into an aesthetic, ball-like shape. However, it can also sometimes assume a more sprawling form.
Description
Bidens hawaiensis is a medium-sized (up to about 6 feet [2 m] in height) perennial herb that can become somewhat woody at its base and on its older branches. Cultivated plants typically live only a few years; the lifespan of wild plants is uncertain but is likely longer.
The often shiny leaves of Bidens hawaiensis are simple (unlike many of its compound-leaf congeners), lance-like to egg-shaped, and have a serrated margin. They can vary in size from 7 to 16 cm long [Wagner et al. 1990] but are most often about 3 inches (8 cm) long.
Bidens hawaiensis produces multi-branched clusters of daisy-like flower heads about 2 inches (5 cm) in diameter. The flower heads have sterile outer ray florets and inner disk 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). Wild and cultivated plants can be seen blooming year-round.
Pollinated perfect and female florets develop into black (when ripe), wingless, long, and straight achenes (single-seeded fruits). The achenes have two awns (projections) without barbs at one end (see photograph above) [Seeds of Hawaii].
Growth Requirements
General
Bidens hawaiensis is one of the few native Hawaiian Bidens species that has simple rather than compound leaves. It is also among the minority of koʻokoʻolau that still have prominent awns on their achenes, although its awns are not nearly as annoying as those of the introduced, naturalized, and common weed Bidens pilosa (Spanish needle). B. hawaiensis often grows in an aesthetic ball-like shape, both in cultivation and in the wild (see photographs above). However, it can also assume a more sprawling form (i.e., be wider than it is tall). Because cultivated koʻokoʻolau typically only live a few years, use your plant(s) as a landscape accent rather than trying to create a permanent hedge or groundcover, or you can keep it/them in a container for easier pest and disease treatment.
Place your ko‘oko‘olau in the coolest but also the sunniest place available; however, Bidens hawaiensis can survive in more shaded sites. Also, select a location with a consistent (but not strong) breeze. Combined, these will help prevent infections of powdery mildew. While wild B. hawaiensis 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 (Koebele) 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 B. hawaiensis would also grow well in more organic-dominant or cinder-dominant soils or media mixes.
Cultivated ko‘oko‘olau grow fast but typically do not live very long. You can expect your planted Bidens hawaiensis 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. However, my B. hawaiensis have usually fared better than some other species I have grown (e.g., B. torta). 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. The first is the unusual breeding system of many 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. Alternatively (and maybe easier), you can maintain several flowering B. hawaiensis at the same time, increasing the odds that at least one of the plants has perfect florets.
The second problem is Bidens hawaiensis 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. hawaiensis (likely) cannot be successfully pollinated by the introduced, naturalized, and common B. pilosa and B. alba. (There's a bit of uncertainty here because Knope et al. [2013] list B. hawaiensis as one of the native species used in their study [Table 1] but do not list B. hawaiensis in their results of crosses [Table 2].) 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. hawaiensis 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. hawaiensis 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 are attacked by spider mites (most common), aphids, mealybugs, 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. However, the Bidens hawaiensis I (Koebele) have grown have rarely been bothered by any of the above-mentioned pests (with spider mites being the most common) and diseases, making it one of the easier ko‘oko‘olau to grow. However, if you're not as lucky, go to the Pests & Diseases page for methods to control 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. hawaiensis, 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 (e.g., B. hawaiensis). 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 the 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, including B. hawaiensis, will produce vigorous hybrids when crossed with other native Hawaiian Bidens species [Ganders & Nagata 1984]. However, natural (i.e., wild) hybrids between Bidens hawaiensis and other native Hawaiian species have not been documented [Plants of Hawai‘i].
A comparison of one non-native (far left) and three native Hawaiian Bidens achenes (photograph courtesy of 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, hawaiensis, refers to Hawaiʻi Island, where this species is endemically found. The geographic suffix -ensis was added to Latinize the name.
BPK