Over the last few weeks I introduced you to several key members of the Pink family including Lychnis, Silene and Saponaria. This article will introduce the less well-known members of the Pink family which include such genera as Agrostemma, Arenaria, Cerastium, Paronychia, Petrorhagia and Sagina. These are primarily alpine plants so if you are a rock gardener, this article will be of particular interest.
(Editor's Note: This article was originally published on July 4, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Over the last three weekends I introduced you to several key members of the Pink Family, Caryophyllaceae, including the genera Lychnis, Silene and Saponaria. I covered the genus Gypsophila several months back and the Pinks (Dianthus) themselves, well, they are on the radar! In this article I will describe the miscellaneous members of the Pink family. As a whole, these plants prefer well-drained, sunny sites with soils on the alkaline (sweet) side.
Agrostemma, the corn cockle, is an annual species native to the Mediterranean region. At one time it was considered a weed among cereal crops. Its seeds are poisonous thus potentially dangerous if accidentally harvested along with wheat, oats and the like. Today, cleaner seeds and use of herbicides have largely eliminated this plant as a agricultural pest and the plant is now enjoying life as a garden ornamental. The relatively large, pink flowers are produced all season, especially if regularly dead-headed. They grow 60-90 cm. The cultivars ‘Milas', ‘Milas Cerise' and ‘Milas Rosea' are the standards in the trade. This annual appears far more popular in Europe than North America.
Details of corncockle or Agrostemma
Arenaria, or sandworts, are primarily white-flowered, mat-forming species that are subjects for the rock garden. The vast majority of the 160 or so species, are either weeds or not particularly garden-worthy. In recent years, several species of Arenaria have been separated into the genera Minuartia or Moehringia. Only botanists can appreciate the subtle differences so I will describe them all as Arenaria. There are only about three somewhat commonly grown species. By far the most attractive is the alpine sandwort, A. montana. This European species looks very much like a Cerastium but has entire petals rather than the cleft petals characteristic of Cerastium. Plants reach 10-15 cm and produce a mat studded with relatively large white flowers in early summer. Arenaria purpurascens is another desirable mat-forming alpine with masses of pale purple or white flowers. Finally, there is A. tetraquetra. This hard mound-forming alpine has short, stiff leaves arranged in a cross-pattern. Superficially it looks more like a Sedum or trailing Hebe or even a green rock! The white flowers are not prolifically produced but the growth habit has enough interest to make this species garden-worthy. These sandworts are rated for zone 4-5.
Details of A. purpurascens, A. montana and A. tetraquetra
The Cerastium or chickweeds, are, like Arenaria, mostly weedy species. There are only two species commonly grown in the garden and one of them in itself, can become a pest under certain circumstances. Snow-in-summer, C. tomentosum, is a trailing species that is a garden bully. In the rock garden, it behaves like a tidal wave, swamping any timid neighbors. However, as a groundcover on slopes or dry sites, it can work quite effectively. Their white flowers are produced in great masses atop wiry 10-15 cm stems. However, the selling point of this plant are its silvery-hairy leaves. Much tamer is the alpine chickweed, C. alpinum, which stays much smaller yet has similar white flowers. The variety ‘Lanatum' has super hairy foliage but prefers winters on the dry side. Both species are rated hardy to zone 3.
Details of C. tomentosum (left and center) and C. alpinum 'Lanatum' (right)
Paronychia, commonly known as nailwort or whitlow-wort, is a rather obscure genus which in leaf and growth habit, could easily be mistaken for a creeping thyme. There are only a few species in cultivation including P. kapela, P. capitata, P. argentea and P. pulvinata. These species produce tiny white flowers surrounded by silver-papery bracts. They are really plants for the alpine enthusiast and require reasonably dry winters to thrive. They can survive to zone 4.
Details of P. kapela
Petrocoptis were once included under Silene. They have pink flowers on trailing stems. Again, they are generally only grown by alpine enthusiasts and are relatively difficult to find. The two species you may encounter are P. hispanica and P. pyrenaica. Both are charming plants well worth searching for if you love alpines.
Details of Petrocoptis pyrenaica (left) and P. hispanica (middle, right)
Petrorhagia saxifraga or tunic flower, looks almost like a small baby's-breath or Gypsophila. Plants are somewhat tufted and reach 30 cm. They are covered in tiny pink flowers all season and appear like a pink fluff in the rockery. They are considered perennial but best treated as biennials. They will self-seed in the garden to maintain their presence.
Details of tunic flower or Petrorhagia saxifraga
Finally we come to Sagina, commonly known as pearlwort or Irish moss. Again, most species are weedy but one species, S. subulata, is enjoying garden-life as a popular subject for planting between stepping stones and patio blocks. This species comes in two color forms; deep green and bright yellow (the cultivar ‘Aurea'). Tiny white flowers are produced in early summer but it is the tight, low foliage that is the selling feature.
The two colour forms of Irish moss, Sagina subulata
I have now covered most of the ornamental species of the pink family (with Dianthus being a notable exception which I plan to rectified in the coming weeks). I hope this series of articles will encourage you to grow more of this wonderful plant family in your gardens.
I would like to thank the following DG members for the use of their pictures: altagardener (Petrocoptis pyrenaica), Calif_Sue (Cerastium tomentosum flower), growin (Petrocoptis hispanica), John_Benoot (Arenaria montana), lilystorm (Agrostemma), philomel (Agrostemma), poppysue (Petrorhagia closeup), weezingreens (Petrorhagia while plant) and Xenomorf (Cerastium tomentosum foliage)
About Todd Boland
I reside in St. John's, Newfoundland, Canada. I work as a research horticulturist at the Memorial University of Newfoundland Botanical Garden. I am one of the founding members of the Newfoundland Wildflower Society and the current chair of the Newfoundland Rock Garden Society. My garden is quite small but I pack it tight! Outdoors I grow mostly alpines, bulbs and ericaceous shrubs. Indoors, my passion is orchids. When not in the garden, I'm out bird watching, a hobby that has gotten me to some lovely parts of the world.