Native Plants of Hawai‘i - Abutilon sandwicense

Abutilon sandwicense

Malvaceae or Mallow family

Synonyms: Abortopetalum sandwicense, Abortopetalum sandwicense var. welchii, Abutilon sandwicense var. welchii

No known ancient Hawaiian name

(see Hawaiian Name below)

Green-flowered abutilon, Greenflower Indian mallow

Natural Range & Environment

Abutilon sandwicense is an endangered shrub endemic to O‘ahu, specifically to the Wai‘anae Mountain Range. It has historically been seen along nearly the entire length of the range on both its windward and leeward sides, from 149 to 875 m (489 to 2,871 ft) where it grows on steep slopes or gulches in mesic forest [ECOS].

At the time of its federal listing as endangered, there were 300 to 400 known wild Abutilon sandwicense. Since then, the wild population size has fluctuated between 137 in 2011 to 527 in 2019; the number of subpopulations has also fluctuated. The last USFWS 5-Year Review [2024] estimates the wild population size at 155 mature and 254 immature plants. USFWS attributes this fluctuation (and possible decline) to the species' relatively short lifespan (likely less than ten years), climate change (i.e., drying), and other threats such as wildfires, ungulates, and alien plant competition. Fortunately, A. sandwicense is actively managed by the US Army's Natural Resources Program O‘ahu (ANRPO) and the Wai‘anae Mountains Watershed Partnership (WMWP), with additional help from other State, Federal, and private agencies and nurseries. Several wild subpopulations are currently protected by fencing, firebreaks, as well as rodent, snail and slug, and alien plant control activities. Additionally, thousands of seeds have been collected and stored, and there have been several reintroduction and augmentation outplantings [USFWS 2024].

While sometimes referred to as the "Green-flowered abutilon," flower color is actually quite variable in Abutilon sandwicense. Above are three examples (Green and mostly-red flower photographs courtesy of Joel Lau ©.). Abutilon sandwicense is the largest (in stature, as well as leaf, flower, and fruit size) of the three Hawai‘i endemic (and endangered) Abutilon (Photo-comparison courtesy of T. Motley via G.D. Carr ©.). A large mature cultivated Abutilon sandwicense.

Description

Abutilon sandwicense is a large (up to about 10 feet [3 m] tall) endangered shrub with a lifespan exceeding five years but probably less than ten. It has light gray bark and soft white wood.

The large (up to nine inches [23 cm] long) heart-shaped leaves of Abutilon sandwicense are pale green with shallowly toothed margins. Much of the plant (i.e., leaves, flowers, and young stems) is covered with nearly invisible hairs.

Abutilon sandwicense produces solitary five-petaled perfect (bisexual) flowers — the largest of Hawai‘i's native Abutilon (see photograph above for comparison) — that typically hang facing downward. Unfortunately, the flowers are often obscured by the plant's large leaves. While commonly called the "Green-flowered abutilon," flower color in A. sandwicense is quite variable, with individual plants displaying flowers with a mix of colors anywhere from nearly all greenish yellow to predominantly dark red (see examples above). Cultivated plants can produce flowers throughout much of the year but typically display the most flowers during the spring. Pollinated flowers develop into multi-chambered green fruits/capsules that dry and turn dark when ripe. The top of the ripe fruit normally splits open to reveal three or more fuzzy brown seeds within each chamber.

Growth Requirements

General

Abutilon sandwicense has many of the same growth characteristics, requirements, and pests as its sister species, Abutilon menziesii (koʻoloa ʻula), but, unfortunately, has yet to become as popular and common in Hawai‘i landscapes. Use this large shrub as an accent, or planted several feet apart, as an informal (i.e., lightly pruned) screen or hedge. It can also be kept as a container plant. However, you will need to transfer it to larger and larger pots if you want it to attain anything close to its full size (i.e., about 10 feet [3 m]).

Abutilon sandwicense does best when planted in a site that receives full sunlight for all or most of the day. However, because it has adapted to a forest habitat, you can also plant it in a lightly shaded area, a choice that might even be preferable if the planting site is naturally hot and dry.

Abutilon sandwicense requires more water than A. menziesii, but not much more. It seems to grow best when the surface soil is dry most of the time but the subsurface (i.e., 2 to 3 inches down) soil remains moist. Therefore, how much you water your plant will depend upon the natural rainfall in your area. As with most native Hawaiian plants, the soil should drain water easily. A. sandwicense is somewhat tolerant to drought, and, fortunately, will let you know with droopy leaves if it needs more water well before it starts dying. We have only grown this species in rocky clay- and organic-dominant soils and in pots with cinder-rich media. Therefore, we're unable to comment on how it would do in more coastal soil types (i.e., sandy or coralline).

Under the optimal growing conditions described above, Abutilon sandwicense grows quickly, and you should have a three-foot (1 m) tall and wide shrub in one to two years. Expect to see your first flowers in about three years. It will likely take five or more years to get a full-sized plant like the one in the photograph above. In-the-ground plants require minimal to no fertilization. In fact, you should avoid regular fertilization since it's likely to produce plants with unnaturally large and floppy leaves, fewer flowers, and more pest problems. If you intend to keep your A. sandwicense in a container, apply only the minimal amount of fertilizer (either balanced controlled-release or foliar) to keep its leaves from yellowing. Hand prune your plant to remove dead or pest-infested branches or to attain a desired shape. However, pruning should be done gradually (i.e., over weeks) to avoid any stress (which can invite pests like black twig borers).

Unfortunately, Abutilon sandwicense don't live forever, and you can expect to see signs of senescence at about the ten-year mark, sometimes sooner. Therefore, be sure to start collecting seeds or rooting cuttings after your plant is a few years old; refer to the guidelines for koʻoloa ʻula within the Native Hawaiian Garden website. If you collect seeds, be mindful that A. sandwicense can hybridize with other Abutilon species. Therefore, it's essential you follow a strict protocol to prevent cross-pollination with any surrounding Abutilon (even if you don't see any). Do this by securely placing a small paper bag around the entire flower just before it begins to open. Use a paper bag, not a mesh bag, since small insects can get through the mesh. Daily, open the bag to discover if the flower has opened. When it does, hand-pollinate the flower either with its own pollen or with pollen from another A. sandwicense. Then, re-close the bag. A few days later, after the flower's petals have fallen away, you can safely remove the bag and let the fruit develop to maturity.

Pests and Diseases

Chinese rose beetles love to chew holes in the leaves of Abutilon sandwicense, and black twig borers will attack and kill its stems, particularly on plants planted in a windless site or those under stress (e.g., drought, over-pruning). Sap-sucking pests like aphids and mealybugs will occasionally infest the growing tips of A. sandwicense, particularly if the plant is over-fertilized. Some growers have reported problems with snails and slugs. Refer to the Pests & Diseases page for methods to control/eliminate each of these pests.

Uses

Ancient Hawaiian

To date, there is no known ancient Hawaiian name for Abutilon sandwicense. Therefore, it's currently impossible to attribute any ancient Hawaiian use(s) to this plant.

Modern

Special Features and Information

General

Abutilon sandwicense is a relative of the more familiar hibiscus, both belonging to the Mallow family (Malvaceae), which contains about 4,225 species within 243 genera. Family members include herbs, shrubs, and trees found worldwide, but most commonly in the tropics. Some of the more economically important species include: cotton (Gossypium spp.), cacao (Theobroma cacao), linden (Tilia spp.), durian (Durio spp.), Hibiscus, and okra (Abelmoschus esculentus) [Britannica;Malvaceae].

There are some 200 Abutilon species worldwide, found primarily in the tropics and subtropics [WikipediA;Abutilon]. In Hawai‘i, there are four native Abutilon species: the indigenous Abutilon incanum, and three endemic endangered species, A. eremitopetalum, A. menziesii, and A. sandwicense.

Abutilon sandwicense is the largest (in stature, as well as leaf, flower, and fruit size) of the three Hawai‘i endemic (and endangered) Abutilon.

While wild natural hybrids between the two endemic Abutilon, A. sandwicense and A. menziesii, have not been seen, artificial hybrids between the two species have been produced [Joel Lau, per. comm]. This could potentially become a problem in the future if the two species' ranges expand and begin to overlap. Perhaps a greater threat is the possible hybridization between A. sandwicense and the introduced and naturalized A. grandifolium (hairy Indian mallow) which is found in the Wai‘anae Mountain Range [USFWS 2024].

Hawaiian Name

Abutilon sandwicense is infrequently called koʻolua maʻomaʻo or koʻolua ʻōmaʻo. These are likely recent adaptations of the ancient Hawaiian name for the closely related koʻoloa ʻula (Abutilon menziesii) since both maʻomaʻo and ōmaʻo can mean "green" in Hawaiian [Pukui & Elbert 1986], and probably refer to the plant's flower color. However, there's no evidence these are ancient Hawaiian names, and the true Hawaiian name for A. sandwicense is yet unknown.

Etymology

Abutilon comes from the Arabic word abū-ṭīlūn (أبو طيلون), which means "Indian mallow." The name was first used in the 18th century as a Neo-Latin word [WikipediA;Abutilon]. The species name, sandwicense, refers to the "Sandwich Islands," as the Hawaiian Islands were once called and named by James Cook on one of his voyages in the 1770s. James Cook named the islands to honor John Montagu (The fourth Earl of Sandwich) for supporting Cook's voyages [Gledhill 2008].

BPK