Native Plants of Hawai‘i - Argemone glauca

Argemone glauca var. decipiens & var. glauca

Papaveraceae or Poppy family

Synonyms: Argemone glauca var. inermis

Pua kala

Kala, Naule, Pōkalakala

Beach poppy, Hawaiian poppy, Hawaiian prickly poppy

Natural Range & Environment

There are two formal varieties of Argemone glauca. Variety decipiens, the rarer of the two varieties, is found in dry to subalpine woodland on the leeward side and saddle area between Mauna Kea and Mauna Loa of Hawaiʻi Island from 610 to 1,900 m (2,001 to 6,234 ft) [Wagner et al. 1990]. Variety glauca grows from sea level to 520 m (1,706 ft) in leeward coastal dry areas on Lehua Island and all the main Hawaiian Islands [Flora of the Hawaiian Islands], being recently rediscovered on Kaua‘i [Lorence et al. 1995]. On Hawaiʻi Island, this variety is supposedly restricted to South Point (Ka Lae) [Flora of the Hawaiian Islands]; however, photographs on iNaturalist.org suggest its range on Hawaiʻi Island may be wider.

Variety glauca can have lots of prickles (photograph courtesy of Forest & Kim Starr CC BY 3.0) or almost none (photograph courtesy of Matthew Kahokuloa Jr. CC BY-NC 4.0). Variety decipiens (last photograph) has many more prickles on its fruit capsules than var. glauca (photograph courtesy of sea-kangaroo CC BY-NC-ND 4.0).

Within each pua kala fruit capsule are dozens of tiny round black seeds (photograph courtesy of J.B. Friday ©) that are easily dispersed by the wind and rain. The seeds sprout into small odd-looking seedlings (see header photograph) that sometimes pop up in unlikely places. Here, several pua kala decorate the edge of a home garden, potentially protecting the other native plants from intruders.

Description

Argemone glauca is a herbaceous plant with a toxic bright yellow sap that grows to as much as 6 feet (2 m) tall; however, it's more common to see mature plants about 3 feet (1 m) tall. The base of its stems can become somewhat woody. Wagner et al. [1990] and others have described pua kala as a perennial. However, in our experience, this colorful herb is more often an annual when cultivated.

The two formal varieties of Argemone glauca are separated morphologically by the number of prickles on the plant's fruit capsules, with variety decipiens having about twice as many prickles as variety glauca: over 100 on each valve and 60 to 80 on each sepal for var. decipiens versus 35 to 65 per valve and 12 to 30 per sepal for var. glauca [Wagner et al. 1990]. In general, both varieties have sharp prickles on their branches, leaves, and fruit capsules. However, some non-formal varieties or forms have few to no prickles on these organs (see photograph above).

Pua kala leaves are deeply lobed, 8 to 21 cm (3 to 8 in) long [Wagner et al. 1990], and usually have a bluish-waxy color, often with a silver or white cast. Stems are typically the same color as the leaves. Leaf margins are irregularly toothed, with each tooth often ending with a prickle.

Pua kala has large flowers (about 3 inches [7.6 cm] across) with bright white petals surrounding a center of bright yellow stamens (male flower parts) and purple stigma (female flower part); they lack fragrance. Plants appear to be self-fertile. Each delicate flower lasts only a day and will wilt almost immediately after being picked. Blooming is nearly continuous for mature cultivated plants until shortly before their senescence and death. Because of its prickly leaves, the introduced and naturalized Mexican prickly poppy (Argemone mexicana) is sometimes mistakenly identified as pua kala. However, the Mexican prickly poppy always has bright yellow petals, while the petals of pua kala are white.

The pollinated flowers of pua kala develop into 1- to 2-inch (2.5- to 5-cm) long oblong fruits that turn dry and brown and split open at their tops when ripe. Inside each fruit capsule, which is usually held upright, are dozens of tiny round brown to black seeds that spill out to the ground when the capsule is shaken by the wind (see photograph above).

Check out this great short TikTok video by laulimhawaii about pua kala. For a longer video, check out the YouTube video by Jill Wagner (Hawai‘i Forest Institute).

Don't be fooled by the Mexican prickly poppy (Argemone mexicana), which has naturalized (now grows wild) on most of the main Hawaiian Islands (photograph courtesy of Dinesh Valke CC BY-SA 2.0). It has a flower with yellow petals, while the petals of pua kala are white.

Growth Requirements

General

Argemone glauca, with its otherworldly colored foliage and bright flowers, is a fascinating addition to any landscape. And, we believe, any negatives attributed to its prickles are overstated. Yes, the prickles are painful to the touch, but they are also much less dangerous than the thorns of popular landscape plants like cacti, roses, and bougainvillea. Perhaps the only true downside to pua kala is its short lifespan, but we offer a partial solution to that below. Use a lone pua kala as a landscape accent or plant several together to more clearly attract attention. Creative gardeners can even strategically plant pua kala to discourage people and pets from invading a garden. Greg Koob has suggested planting pua kala under windows to discourage burglars [Hawaii Horticulture]. You can also keep pua kala in a container where it will flower but will likely become root-bound and stunted.

Plant your pua kala in a site with lots of full sunlight for the best growth, color (i.e., maximum blue-silver), and most flowers. Avoid windy sites because pua kala tends to get blown over. This normally doesn't kill the plant but could place it somewhere you don't want, like across a walkway. Secure a stake along the plant's central stem to prevent it from toppling or to straighten a fallen plant.

Pua kala is extremely heat and drought tolerant. Therefore, once established in the ground, water it very little or not at all. Too much watering can result in top-heavy plants, which tend to fall over, and possible stem and root rot. If you do water your pua kala, do so with infrequent (e.g., once a month) long deep waterings rather than short frequent showers; the surface soil should be dry most of the time.

We have successfully grown pua kala in cinder/lava, clay, and organic-dominant soils; Greg Koob states that pua kala will also grow in sand [Hawaii Horticulture]. Make certain the soil does not become waterlogged for more than a day. In a container, use a media mix with a lot (50% or more) of black cinders or perlite.

We have not found it necessary to fertilize pua kala and actually discourage fertilizing because it can result in excessive growth (and toppled plants). After a primary stem has aged and begun to wither, prune it back to the plant's base to encourage new shoots. You can also try removing the top half of the primary stem to encourage new shoots (i.e., more stems and flowers). Removing young fruits (capsules) and old flowers regularly also seems to extend blooming.

Eventually — about a year in our experience — your pua kala will die, and then the question becomes, "What to do next?" If you enjoy propagating plants, try collecting seeds early and sowing several in a pot filled with clean, well-draining media — then wait. Pua kala seeds can remain dormant in the soil or media for many months. Scarification, pre-soaking (in hot water), and gibberellic acid [Seeds of Hawai‘i] pre-treatments may speed germination, but there is also some evidence that sprouting is influenced by day length, with the shorter days of November and December being the trigger [Culliney & Koebele 1999]. Alternatively, you can dedicate a spot in your landscape to pua kala, permit (or help) your plant(s) to scatter its seeds within this spot, and water the area regularly AFTER the adult plant(s) has died. With a bit of luck, each year, some of the seeds will sprout, and you will have a recurring patch of pua kala to always decorate the space. Depending on the number of sprouts, you may want to do some thinning or repositioning. Fortunately, the tiny seedlings normally survive any early transplanting.

Pests and Diseases

Pua kala's toxic sap seems to deter most pests, although I (Koebele) have seen the occasional spider mite infestation. Refer to the Pests & Diseases page for treatments. Avoid overwatering because this can result in root and stem rot.

Uses

Ancient Hawaiian

Hawaiians used the bright yellow sap of pua kala to ease the pain of toothaches, ulcers, and nerve-related diseases [Krauss 1993]. Additionally, Degener [1973] states that the sap was used to treat warts.

Modern

A few people have told me (Koebele) over the years that they use pua kala for pain relief. However, we strongly urge you to consult with your doctor before using pua kala medicinally. Also in modern times (and perhaps ancient), pua kala is used to decoratively stain fabrics. Watch this short Instagram video by kapacurious to see exactly how this is done.

Special Features and Information

General

The Poppy family (Papaveraceae) contains about 42 genera and approximately 775 known species worldwide, occurring in temperate and subtropical climates, mostly in the Northern Hemisphere. Most members of the family are herbs, with a few shrubs and small trees. While many species are popular as ornamentals, only two species are economically important: Papaver somniferum, cultivated to produce morphine and other opiates, and Papaver bracteatum, for the production of thebaine [WikipediA; Papaveraceae].

Pua kala is the only poppy native to Hawaiʻi and is closely related to the Mexican poppy (Argemone mexicana), which has naturalized (grows wild) in the Islands. A spontaneous hybrid between the two species was collected in upper Pāʻia, Maui, but did not produce seed [Wagner et al. 1990].

Pua kala is one of the few truly toxic native Hawaiian plants. We could find only one limited study that investigated the chemistry of the sap of Argemone glauca. This study by Stermitz et al. [1971], along with other more comprehensive studies of the closely related Argemone mexicana, determined that the two species contain an assortment of alkaloids that are likely responsible for their toxicity and medicinal uses. However, neither species appears to contain the well-known opioids, such as morphine or codeine, extracted from the sap of their more-distantly related cousin species, the opium poppy (Papaver somniferum).

According to Scott & Thomas [2000], the alkaloids in pua kala supposedly taste extremely bitter (neither of us has been brave enough to taste it), thus limiting the number of reported poisonings. The alkaloids also reportedly irritate the stomach and intestines. This acrid taste is likely the reason cattle (and, possibly, other ungulates) find pua kala unpalatable; it is one of the few native plants left untouched in cow pastures. Perhaps pua kala's unpalatability could be used to create a natural behavioral barrier to prevent unwanted grazers from entering fragile native areas.

Several online sources highlight pua kala as a "fire-tolerant" plant that repopulates areas burned by wildfires in an exceptional way. However, while a study by Loh et al. [2009] showed that pua kala seeds can survive, sprout, and grow to maturity after a wildfire, they were not alone in this ability and that five other species (i.e., Bidens hawaiensis, Canavalia hawaiiensis, Dodonaea viscosa, Sida fallax, and Sophora chysophylla) were similarly capable.

Hawaiian Name

In Hawaiian, Pua means “flower,” while one of the meanings for Kala is “rough” [Pukui & Elbert 1986]. Pukui & Elbert [1986] also state that, as a stative verb, Kala and Kākala are equivalent and that one meaning of Kākala is “thorny.” Therefore, Pua kala can be translated as “rough flower” or “thorny flower.”

Pua kala shares its name with a native lobelia (Cyanea solenocalyx) endemic to Molokaʻi, which also has prickly leaves, and a European weed, the spear thistle (Cirsium vulgare), that has become naturalized on all the main Hawaiian Islands [Flora of the Hawaiian Islands]. The name pōkalakala is shared with Polyscias lallani (syn. Munroidendron racemosum), an endangered tree endemic to Kaua’i.

Etymology

The genus name, Argemone, is derived from the Greek word argema, for cataract, in reference to the use of the sap of a poppy-like plant with the same name reputed to cure cataracts [Wagner et al. 1990]. The species and variety name, glauca, is from the Greek word for "sea-green, bluish, or with a waxy bloom," referring to the color of this poppy's leaves. The subspecies name, decipiens, is from the Latin word deceptum, which means "deceptive or misleading" [Gledhill 2008], possibly referring to the deceptive similarity of this variety to var. glauca.

BPK