This week’s Friendly Friday challenge theme is ‘The Color Pink.’ See more responses here.

Pinkhead smartweed (Polygonum capitatum or Persicaria capitata) is a groundcover that hails from western China and the Himalayas. It’s variously known as pinkhead knotweed, pink knotweed, Japanese knotweed, pink-headed persicaria, or pink bubble persicaria. I use pinkhead smartweed for the very good reason that I like the name. It sounds like the name of someone pretentious, but slightly seedy, from the alleged upper crust of society.

In this bounty of names, a couple of elements stand out. One is ‘pink,’ the other is ‘weed.’ This is a very pink plant and, in Hawaii and elsewhere, an invasive weed. Drive eastbound over Saddle Road (officially Hawaii Route 200, the Daniel K. Inouye Highway) and, once you cross the saddle and begin your descent, this plant will become obvious very quickly. It lines the road on both sides for several miles with very little in the way of other plants competing for that space. This is because pinkhead smartweed will grow in poor ground and lava fields fit that description.

This is also a stretch of highway that, relatively recently, was converted from a narrow, winding road, that rental car companies routinely forbid their clients from driving on, to a wide, smooth thoroughfare, the only place on the island where you can legally go 60 mph, and where you can expect to receive a ticket if you go 80 mph like everybody else.

Redoing the road left verges of rock and gravel and very little else. Pinkhead smartweed was quick to move in and colonize this unpromising territory so that now the descent toward Hilo begins with pleasing pink borders.

The top photo shows the rugged kind of ground pinkhead smartweed can grow in. To the right, bees appreciate the flowers of this plant growing at an elevation over 5,000 feet. Below, the collapse of a lava tube has left a shady hole where pinkhead smartweed, an endemic amaumau fern, and an ohia tree have established a good foothold.