Native Plants of Hawai‘i - Bidens mauiensis

Bidens mauiensis

Asteraceae or Sunflower family [Five-minute families]

Synonymns: Bidens awaluana, Bidens mauiensis var. ciliata, Bidens mauiensis var. cuneatoides, Bidens mauiensis var. forbesiana, Bidens mauiensis var. lanaiensis, Bidens mauiensis var. media, Campylotheca mauiensis, Coreopsis mauiensis

Koʻokoʻolau

Kokolau, Kōʻokoʻolau, Koʻolau

Maui beggarticks

Natural Range & Environment

Distribution: L/ M/ Ka

Bidens mauiensis is relatively common on coastal bluffs, lithified sand dunes, and in shrubland vegetation on dry slopes from about 165 to around 1970 feet.

Bidens mauiensis has the typical daisy-like flowers common to all the native Hawaiian Bidens. However, reportedly, the flowers near the end of the flowering season are noticeably smaller than those at the beginning. B. mauiensis is a small prostrate species found in very rocky places (photograph courtesy of Forest & Kim Starr CC BY 3.0 US), sometimes close to the ocean (photograph courtesy of Forest & Kim Starr CC BY 2.0) and sometimes farther inland (photograph courtesy of Forest & Kim Starr CC BY 3.0 US). B. mauiensis is being used on Kaho‘olawe to revegetate areas where digging a planting hole is prohibited because of buried unexploded ordnance (photograph courtesy of Forest & Kim Starr CC BY 3.0 US). A cultivated B. mauiensis doing quite well in David's (Eickhoff) inland garden.

Description

Herbaceous, Short, Less than 1

Flowers noticeably smaller on older plants and at the end of flowering season.

Closely related to B. molokaiensis, but differs in leaf shape and sizes of flower heads. Populations of B. mauiensis from East Maui and Kahoʻolawe are distinctive having rather succulent leaves.

Bidens hillebrandiana is a herb usually less than 1 foot (30 cm) tall. While often compact in shape, particularly when out in full sunlight, it can become more sprawling when shaded. It has been my (Koebele) experience that cultivated plants (in pots) live about three years. While there have been no formal studies, anecdotal observations suggest that wild plants live somewhat longer [USFWS 2023].

The leaves of Bidens hillebrandiana are undoubtedly its most distinctive and attractive feature. They are usually pinnately (occasionally bipinnately) compound or rarely simple with toothed or lobed margins. They are also hairless (or nearly so), fleshy, and shiny, often looking like they were made of plastic.

Bidens hillebrandiana produces clusters of small (less than 1 inch [2.5 cm] across) daisy-like flower heads. The flower heads have sterile outer ray florets and perfect (bisexual) inner disk florets. This is in contrast to many other native Hawaiian Bidens species like B. amplectens, B. hawaiensis, B. menziesii, and B. torta that have inner disk florets that are either perfect (bisexual) or all pistillate (female), in which case the entire plant is female. Both cultivated and wild B. hillebrandiana can be seen blooming year-round.

The two subspecies can be distinguished by their flower heads. Subspecies hillebrandiana has 1 to 3(-4) flower heads per cluster, with each flower stem (peduncle) 2 to 8.5 cm (0.8 to 3.3 in) long, while subspecies polycephala has (4-)5 to 30 flower heads per inflorescence, with each peduncle 0.2 to 1(-2) cm (0.1 to 0.4[-0.8] in) long [Wagner et al. 1990].

Pollinated disk florets develop into black (when ripe), long, straight, and slightly-widened achenes (single-seeded fruits) with two awns at one end (see photograph above and reference links) [Seeds of Hawaii; Seeds of Hawaii].

Growth Requirements

General

Bidens mauiensis has a number of desirable horticultural characteristics. One, it is probably the most drought tolerant of all the native Hawaiian Bidens, making it a great choice for a xeriscape garden. Two, it can tolerate salt spray (since it often grows within a stone’s throw of the ocean), making it a good pick for a native coastal garden (although I don’t know how well it grows in sand). Three, it ‘likes’ to grow in very rocky areas, making it an excellent addition to a rock garden. (No one seems to know why B. mauiensis is typically seen in very rocky sites. It may be it has specific adaptations for this type of substrate, or it may be that it’s not a very good competitor with other plants in other soil types.) Four, it is small, making it the perfect choice as a container plant.

Accent

Container

Flowers noticeably smaller on older plants and at the end of flowering season.

Dry

Soil must be well drained

Full sun

Bidens hillebrandiana reminds me (Koebele) of the small plastic plants my sister would strategically place in the kitchen and bathrooms of her home. And, while I cannot recommend growing this glossy little ko‘oko‘olau in your bathroom, I would bet it would do just fine on a sunny windowsill in your kitchen. Because I have only grown B. hillebrandiana in pots (inside a shadehouse), I cannot comment personally regarding in-the-ground plantings (but see next paragraph). However, I suspect that the salt spray in its natural habitat protects this ground-hugging ko‘oko‘olau from snails and slugs in the wild. Therefore, unless you live right next to the ocean, you should be prepared to protect your in-the-ground B. hillebrandiana from these herbivores (see Pests & Diseases for methods). Because of this potential threat, I recommend keeping B. hillebrandiana in a container.

David (Eickhoff) has kept Bidens hillebrandiana both in pots (terra-cotta and cement to prevent it from toppling over in strong winds) and in the ground. He did not encounter any problems at his inland home other than the unanticipated shading from a nearby ‘iliahi. As the ‘iliahi grew larger, it eventually and completely shaded the smaller B. hillebrandiana, causing it to decline and eventually die.

Wild Bidens hillebrandiana grow in mesic to wet coastal habitats, which means they are adapted to mostly sunny and windy conditions with readily available soil moisture. Keep this in mind when placing and caring for your ko‘oko‘olau (i.e., a sunny and windy spot with regular watering). However, David (Eickhoff) has noted that established plants exhibit some drought tolerance. Make sure the media or soil surrounding the roots of your B. hillebrandiana easily drains away any excess water. Do this by making cinder, coral rubble, or sand a significant portion of the media mix. Obviously, this shoreline ko‘oko‘olau is quite tolerant of salt spray.

Unfortunately, it has been my experience that cultivated Bidens hillebrandiana (in pots) only live about three years. While there have been no formal studies, anecdotal observations suggest that wild plants live somewhat longer [USFWS 2023]. Typically, within the first year, my ko‘oko‘olau would flower for the first time and, thereafter, would flower sporadically year-round. All my potted B. hillebrandiana received an application of granular controlled-release fertilizer every six months, which I can only guess was helpful since I've never grown this species without fertilization.

Because cultivated ko‘oko‘olau are typically short-lived, you will need to replace them every few years if you wish to keep them long-term. The easiest way to do this is by rooting stem cuttings of your existing plant; B. hillebrandiana cuttings typically root easily. However, propagating ko‘oko‘olau from cuttings doesn't entirely "set back the clock" on these short-lived perennials, and these cloned plants sometimes lack the vigor of ko‘oko‘olau propagated from seeds. Also, unlike seeds, you cannot easily store 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 (see Description above). However, according to Wagner et al. [1990], Bidens hillebrandiana may be one of the endemic Hawaiian Bidens that only produces flower heads with perfect (bisexual) florets (i.e., no female plants), which makes collecting seeds a bit easier since you potentially only need to keep one plant in order to get viable seeds (although keeping two or more genetically different plants so they can cross-pollinate would obviously be better).

The second problem is that Bidens hillebrandiana can successfully hybridize with other native Bidens species [Ganders & Nagata 1984; Plants of Hawaii]. This makes collecting seeds of known genetic identity a challenge. Fortunately, a study by Knope et al. [2013] showed that B. hillebrandiana 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. hillebrandiana 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. hillebrandiana 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

Perhaps the same pests that affect other native Bidens spp. such as spider mites, aphids, scale, spittle bugs, slugs and snails.

Ko‘oko‘olau in general are attacked by spider mites (most common), aphids, lace bugs, 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. The Bidens hillebrandiana I (Koebele) have grown remained relatively pest- and disease-free except for spider mites. However, as noted above, I have only grown this species in pots within a shadehouse. Refer to the Pests & Diseases page for methods to control all the above-mentioned pests and diseases.

If you plan to harvest leaves from your koʻokoʻolau to make tea, be sure you have not used any systemic or otherwise long-lasting pesticides or fungicides in the past that could potentially still be present in or on the leaves. Rather, use only short-term and less toxic chemicals like insecticidal soap and baking soda, and be sure to wash the leaves before making your tea.

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 containing 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 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 native 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 that are 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 will produce vigorous hybrids when crossed with other native Hawaiian Bidens species [Ganders & Nagata 1984]. Additionally, natural hybrids between Bidens hillebrandiana subsp. polycephala and B. molokaiensis and B. micrantha have been recorded [Plants of Hawaii; Starr Environmental].

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 (single-seeded fruits) [Wagner et al. 1990]. However, it's important to note that some Bidens species have no awns (e.g., Hawaiian endemics) while others, like B. pilosa, can sometimes have more than two awns [Flora of Australia].

The species name, mauiensis, refers to the island of Maui, one of the three Hawaiian islands where this species is endemically found. The suffix -ensis was added to Maui to Latinize the name [Gledhill 2008].

BPK