Hawaii: Mauna Kea silversword, the rarest plant I’ve ever seen

On one of the last days of our Hawaii vacation I got to see one of the rarest plants I’ll every lay my eyes on: the Mauna Kea silversword (Argyroxiphium sandwicense ssp. sandwicense). Like its close relative, the Haleakalā silversword we saw last year on Maui (Argyroxiphium sandwicense ssp. macrocephalum), the Mauna Kea silversword is critically endangered. Once abundant on the upper slopes of Mauna Kea on the island of Hawaii, there is now only one naturally occurring population with about 40 plants. Heroic efforts have been made in the last decades to save the Mauna Kea silversword from extinction by reintroducing seed-grown plants into the wild; today, about 8,000 plants are growing on Mauna Kea.

The Mauna Kea silversword lives in a forbidding environment: a wind-swept alpine desert above 8000 ft. with thin volcanic soil, strong UV radiation, virtually zero humidity, extreme drought in the summer and a total annual precipitation of 8-10 in. (mostly in the form of snow in the winter). Temperatures can drop below freezing any time of the year. At the upper range of its native habitat, nothing else grows.

All the Mauna Kea silverswords you see in this post were photographed in a special enclosure at the Mauna Kea Visitor Information Station (9,175 ft). This is as far as most passenger cars can go; a mostly unpaved 4WD road leads to the summit of Mauna Kea (13,803 ft.) where the world’s largest astronomical observatory is located. Our rental car was neither authorized nor able to maneuver the rough road. (Click here to watch a video about visiting Mauna Kea; it’s 8 minutes well spent.)

The ʻAhinahina Enclosure at the Visitor Information Station (ʻahinahina is the Hawaiian word for any of the five silversword species and subspecies) looked just like an animal corral. Except the goal is not to keep animals in, but out.

All of the plants in this enclosure have been reintroduced. Larger clumps are easily visible, but smaller plants are marked with yellow flags. Read this article about a silversword “planting party” in May 2013. The survival rate of reintroduced plants is above 85%, giving hope that the Mauna Kea silversword can be pulled back from the brink of extinction.

The silversword was once so common on the slopes of Mauna Kea that cowboys “sang songs about the blinding glare from the reflection of the sun on their leaves” (1). Over the decades, feral cow, sheep and goat populations—descendants of animals introduced to the islands in the 1790s—began to expand into the higher reaches of Mauna Kea, devouring all the silverswords in their path.

The decline of the Mauna Kea silversword was first documented in 1892; a hundred years later, the University of Hawaiʻi Botany Department published a photo showing the only known natural population consisting of only a few plants.

Rescue efforts began in the 1970s, initially with modest success. Over the years, scientists refined their methods. Now they hand-pollinate flowering plants both in the greenhouse and in the field to increase genetic diversity. This often involves rappelling down steep cliffs to get to flowering plants growing in the wild. But the efforts are paying off, and the outlook for this archetypically Hawaiian native is brighter than it was 20 years ago.

The Mauna Kea silversword is a member of the silversword alliance, a group of 50 species in the sunflower family that are all endemic to the Hawaiian islands and can be traced back to one common ancestor (a California tarweed) from which they rapidly developed.

The silversword forms clumps of rosettes which, like most agaves and some other succulents, are monocarpic: They die after they flower. Typically it takes 6-12 years for a rosette to flower, although some reports claim the plant lives 40-50 years before it send up its beautiful but terminal flower spike.

On Maui we saw Haleakalā silverswords in bloom. No such luck with the Maunea silversword. All I saw was dead flower stalks (and rosettes) and a single individual with an emerging spike. See photos at the bottom of this post.

But I did see plenty of healthy rosettes. They were so ethereal, they looked like they had come from another planet.

The leaves have a bright silver sheen with hints of turquoise. More than once I had to look close to assure myself that they weren’t made of metal. I’ve never seen a plant that looks quite like this.

On closer inspection, you can see that the leaves are made up many layers of very fine hairs that reflect the intense sunlight.

I was so fascinated by the Mauna Kea silversword, that I took a lot of photos. Here are some more:

The clump in the next photo must have had a couple of rosettes that flowered and died.

Here is a clump with dried up flower spikes:

And this is the only plant in the ʻAhinahina Enclosure that had an emerging flower spike. If we had visited a month later, we would have seen it in flower.

 

 

 

What I wouldn’t give to be able to grow this magnificent plant in my garden. But the plant is so well adapted to its harsh habitat that it doesn’t survive anywhere else. So unless you live in a high-altitude location on a tropical island and have an unethical insider source that gives you seeds or a live plant, you’ll have to make the trek to Mauna Kea to see the silversword in person.

Finally I’ve got to show you this video I found on YouTube. The poor schmuck thinks he’s filming the Maua Kea silversword when it’s actually an expanse of very common mullein (Verbascum thapsus). I thought it was very funny, especially when he receives an email on his cell phone.