Native Plants of Hawai‘i - Artemisia mauiensis

Artemisia mauiensis

Asteraceae or Sunflower family [Nature Clearly]

Synonyms: Artemisia australis var. mauiensis, Artemisia mauiensis var. diffusa

ʻĀhinahina

Hinahina

Maui wormwood

Natural Range & Environment

Artemisia mauiensis is endemic to East Maui. It is found growing on or near exposed faces of volcanic rock in subalpine shrubland within the crater and on the southern slopes of Haleakalā from 1,900 to 2,300 m (6,234 to 7,546 ft) [Wagner et al. 1990].

Artemisia mauiensis produces panicles of small multi-floret flower heads that turn from yellow to brown as they age (yellow flowers photograph courtesy of Spencer Len Pote CC BY-NC 4.0; brown flowers photograph courtesy of Forest & Kim Starr CC BY 3.0 US). What makes this ʻāhinahina species particularly popular is its lacy silver foliage, thought to protect it from the damaging ultraviolet radiation it receives in its upland natural habitat.

In the wild, Artemisia mauiensis can grow quite large and is frequently wider than it is tall (photograph courtesy of Forest & Kim Starr CC BY 2.0). Old plants often have a gnarled trunk and branches (photograph courtesy of Michael Finch CC BY-NC 4.0). At Auwahi and elsewhere on Maui is an ʻāhinahina previously classified as Artemisia mauiensis var. diffusa (photograph courtesy of Forest & Kim Starr CC BY 2.0) with leaves that look quite different from the silvery A. mauiensis growing farther upland. Many botanists think this is a hybrid between A. australis and A. mauiensis [Wagner et al. 1990].

In Hawai‘i, Artemisia mauiensis does best when planted in cool uplands, either in a semi-natural setting, such as here outside the National Park Headquarters on the road up to the Haleakalā summit (photograph courtesy of Forest & Kim Starr CC BY 2.0) surrounded by other native montane plantings, or in a botanical garden in Kula, Maui, surrounded by colorful alien plants (photograph courtesy of Forest & Kim Starr CC BY 3.0 US). In the continental USA, a cultivar of A. mauiensis called 'Makana Silver' has been tested, given a 5-star rating (photograph courtesy of Penn State University (SEAREC) ©), and sold as a short-lived, fast-growing perennial or annual. It is popular in both public (photograph of A. mauiensis in the United States Botanic Garden courtesy of Daderot Public Domain) and private gardens.

Description

In the wild, Artemisia mauiensis is a shrub that typically grows to be only a few feet tall but can be several feet wide. In contrast, cultivated plants often take on an attractive ball-like shape (see photographs above). In its natural habitat, plants can live longer than five years. However, cultivated plants are typically short-lived, only lasting one to a few years before dying either because of temperature extremes outside their tolerances (e.g., too hot) or other environmental factors (e.g., poor soil drainage). The sprawling branches of old plants can become quite thick and acquire a deeply furrowed bark (see photograph above).

The thin, dissected, and silvery leaves of Artemisia mauiensis are its most distinctive and attractive feature. The leaves have a faint to moderate aroma similar to other wormwoods. And, while never brave enough to taste the leaves, I (Koebele) have been told and read that they are quite bitter. The silver color is due to a dense covering of very short hairs, thought to reduce leaf temperature and water loss and protect the plant from the harmful ultraviolet radiation it is exposed to in its natural subalpine habitat [Wagner et al. 1990].

ʻĀhinahina has small yellow turning to brown, daisy-like flower heads, (i.e., compound flowers) with outer female and inner perfect (bisexual) florets [Wagner et al. 1990] that develop on branched spikes (panicles) that extend above its foliage (see photographs above). Each pollinated floret develops into a small pale brown to gray ribbed cypsela (a type of dry single-seeded fruit) [Seeds of Hawaii].

Artemisia mauiensis can hybridize with other Artemisia species, both native (e.g., A. australis [Wagner et al. 1990; Plants of Hawaii]) and possibly non-native in Hawai‘i; the naturalized mugwort (A. vulgaris) has been successfully crossed with other Artemisia species [James et al. 2000] and even with a chrysanthemum [Deng et al. 2010]. Therefore, if you intend to collect and sprout seeds from your ʻāhinahina, first look around your neighborhood for other Artemisia species and chrysanthemums, and then consider bagging and hand-pollinating your plant to be certain the seeds are genetically pure. The safest way to propagate new plants is to root stem cuttings. However, this requires more effort than rooting A. australis cuttings.

Growth Requirements

General

There are very few native Hawaiian plants that are more commonly grown outside the Hawaiian Islands than within. Artemisia mauiensis is one of these; another that comes to mind is ālula (Brighamia insignis). Perhaps one reason for this is because many homeowners outside Hawai‘i are accustomed to replanting a significant portion of their landscape each spring, while here in Hawai‘i we often assume/expect our gardens to last forever. In the continental USA, A. mauiensis is regarded as a fast-growing, short-lived perennial or annual, unable to survive the winter cold in most places. Here in Hawai‘i, just the reverse is true. For most of us, living in coastal or lowland areas under 1,000 ft (305 m) elevation, the summers are just too hot for A. mauiensis to live for more than a year or two. Only in the uplands (primarily on Maui) do you commonly see A. mauiensis in public and private landscapes survive for anything approaching its natural lifespan. Therefore, if you really love the look of this ʻāhinahina — and you live in a coastal or lowland area — be prepared to propagate or purchase a new plant every year or two.

While Artemisia mauiensis is a shrub, because of its short lifespan in coastal and lowland areas, it's best displayed as a landscape accent or a container plant rather than using it to make a hedge or cover large areas (unless you are planting it in an upland site). A. mauiensis is adapted to intense sunlight in its natural habitat. However, this natural habitat is typically cool and often foggy. Therefore, if planted in a frequently hot, low-humidity site, try to mitigate the drying air by misting your ʻāhinahina regularly, particularly during midday. Placing it in a location that only receives direct morning sunlight can also help.

Wild Artemisia mauiensis sometimes experience drought (and survive). However, again, in a hot, low-humidity planting site, letting the soil or media surrounding your ʻāhinahina dry out is risky. Much safer is to plant your A. mauiensis on a mound of black cinders and regularly water the mound, trusting the porous cinders will prevent the plant's roots from becoming asphyxiated. In a pot, a media mix dominated by cinders is also the best choice. A. mauiensis can endure strong winds but is intolerant of salt spray [Ethan Romanchak, per. comm.].

Planted Artemisia mauiensis can grow quickly to two feet (61 cm) or more in width in less than a year but then seem to slow their growth after they begin producing flowers. I (Koebele) never fertilized my in-the-ground plantings. My potted ʻāhinahina were given a granular, controlled-release fertilizer every six months or so. Pruning is typically not necessary except to remove the occasional dead branch or the panicles of flowers (if you find them unsightly). However, I recommend letting any flowers fully develop and collecting and storing the cypselae (in your refrigerator) to propagate later replacement plants; you can also root ʻāhinahina stem cuttings. See Description above for a caution and advice on collecting seeds and rooting cuttings.

Pests and Diseases

In my (Koebele) experience, most pests seem to avoid ʻāhinahina — except for spittlebugs — maybe because of its aromatic leaves. Others have reported occasional problems with mealybugs, scale insects, spider mites, and whiteflies [Lilleeng-Rosenberger 2005; Hawaii Horticulture]. Refer to the Pests & Diseases page for ways to deal with these pests.

One potential pest not to be eliminated is Trupanea artemisiae, an endemic species of tephritid fruit fly (family Tephritidae) restricted to East Maui. It lays its eggs in the flower heads of native Hawaiian Artemisia species, where the larvae presumably feed and mature [Starr & Starr 2012].

Trupanea artemisiae female (photograph courtesy of National Parks Service Public Domain).

Uses

Ancient Hawaiian

According to Ka‘aiakamanu & Akina [1922], ʻāhinahina, mixed with other plant ingredients, was used to treat asthma, lung problems, and high fevers. Recent chemical analysis supports the efficacy of this ancient use [Zant & Gubler 2014]. While several online sources claim that ʻāhinahina was traditionally placed inside large calabashes (‘umeke) with feathered cloaks to protect the cloaks from insects (a reasonable claim), I (Koebele) have yet to find a reliable ethnobotanical source to substantiate this assertion.

Modern

ʻĀhinahina leaves are occasionally used in lei and flower arrangements [Hawaii Horticulture].

Special Features and Information

General

Asteraceae is a very large family — about 32,000 species within 1,900 genera — of mostly herbaceous plants 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].

There are about 500 species in the genus Artemisia worldwide. Some well-known non-Hawaiian Artemisia species are: Absinth wormwood (Artemisia absinthium) used to infuse absinthe and other spirits; tarragon (A. dracunculus) used in food; several species of the ubiquitous sagebrush of the American West; and the common mugwort (A. vulgaris) used medicinally for centuries [WikipediA; Artemisia]. Here in Hawai‘i, mugwort is frequently used to flavor and decorate Asian foods like rice cakes and soups.

There are three native species of Artemisia endemic to the Hawaiian Islands: A. australis, found on all the main islands; A. kauaiensis, found on Kauaʻi; and A. mauiensis, found on Haleakalā, East Maui. Some botanists think an ʻāhinahina found on Maui and previously classified as Artemisia mauiensis var. diffusa represents a hybrid between A. australis and A. mauiensis [Wagner et al. 1990].

Two young potted ʻāhinahina: Artemisia mauiensis (left) and Artemisia australis (right). Unfortunately, there are no reliable online images of Artemisia kauaiensis at this time that we can repost.

Hawaiian Name

ʻĀhinahina comes from ʻāhina, which means "gray, gray- or white-haired," referring to the plant's color. Hina also means "gray, gray- or white-haired," with Hinahina meaning "very gray" [Pukui & Elbert 1986].

The three native Hawaiian Artemisia species share the names ʻĀhinahina or Hinahina with some other native Hawaiian plants with silvery leaves. ʻĀhinahina and Hinahina are shared with the endemic silversword (Argyroxiphium sandwicense), while Hinahina is shared with several endemic Geranium species, the indigenous hinahina kū kahakai (Heliotropium anomalum), the endemic fern palai hinahina (Hymenophyllum lanceolatum), the endemic hinahina kahakai (Nama sandwicensis), and the indigenous pōhinahina or hinahina kolo (Vitex rotundifolia).

Etymology

The genus name, Artemisia, erected by Carl Linnaeus in 1753, is derived not only from the name of the Greek goddess Artemis (Roman Diana) but also to honor the historical Greek Queen Artemisia II of Caria, who was, among other things, a botanist and medical researcher [Wagner et al. 1990; WikipediA; Artemisia]. The species name, mauiensis, refers to the island of Maui, where this species is endemically found. The suffix, -ensis, meaning "from" or "originating in," was added to Maui to Latinize the name [Gledhill 2008].

BPK