species of phlox have been
mainstream garden plants for many years, but at this time there is
little literature devoted to the group from a horticultural
point of view. Neither of the
two recent horticultural books on phlox is in English (Fuchs
1994, Bendtsen 2003).
Wherry's systematic monograph of the genus is 55 years old. James
Locklear's new book, Phlox: A Natural History and Gardener's Guide,
gives a wealth of information on the ecology and habitats of the wild
species, along with botanical descriptions and colorful descriptions of
the landscapes the plants inhabit.
phlox species have great horticultural potential but are virtually
unknown to the general gardening public. These web pages are an attempt
to bring some of these plants to the attention of gardeners
commercial growers. They are essentially in first draft form. I have
phlox off and on for the last 25 years; most of my experience has been
with the species of the Appalachians.
is a genus of
sixty-some species. There is a current list of taxa at the USDA Plants Database, including
synonomy, common names, and geographic ranges. With the exception of
one species found in northern
Asia, the group is exclusively North American. The genus shows great
diversity in growth form from creeping mat types to erect plants well
over a meter tall. Almost all are herbaceous or semi-woody perennials –
a very few are annuals. Phlox inhabit a diverse range of habitats from
marshes and riverbanks to prairies, deserts, and tundra and a wide
geographic range from Alaska to New England and south to Mexico and
general the larger herbaceous
are grow in moist, open habitats of the eastern and central US and
southern Canada. The forests and prairies of this general area also
support herbaceous species of small to medium size (15-40cm
Barrens in the East and semi-arid and alpine habitats in the West
support many species of low or medium size (5-45cm tall).
flowers of all phlox are attractively colored and showy. They have been
grown as garden plants since the 17th century, when Phlox
paniculata was sent from the American Colonies to Europe. A
few other species, such as P. subulata, P. stolonifera,
and P. drummondii, have become garden subjects, but
surprisingly few of the wide array of wild phlox have come into
mainstream horticulture. Of these, only a couple have been the subjects
of extensive breeding and selection programs. Many cultivars of Phlox
paniculata have been developed primarily in England and The
Netherlands, and these have become important elements of the formal
perennial border. P. drummondii, an annual of the
Texas plains, has been bred for a wide range of flower colors and is a
popular bedding plant started from commercial seed.
is a taxonomically confusing group. The best reference and the
only book devoted to the systematics of the genus is
Edgar T. Wherry’s The Genus Phlox,
1955. Luckily, there has been more recent work on the genetics and
evolution of phlox by Donald Levin and his students at the University
of Texas. Their publications help greatly with the relationships of the
eastern species, at least. The most active worker in the field at the
present time is Carolyn Ferguson at Kansas State University.
into three main sections, based primarily on floral and
seed characters. Section Protophlox is characterized as having short
styles united for ¼ to ½ their length and relatively large seeds
with large embryoes. Section α-Phlox has styles united for more than ½
their length, with the styles often exceeding the length of the
floral tube and relatively large seeds with large to medium sized
embryoes. Section Microphlox is composed of small western and arctic
species with styles united more than ½ their length and relatively
small seeds with small to medium sized embryoes. Wherry's arrangement
divides the eastern moss phlox species, which would otherwise seem by
appearance to be closely related, into two different sections of the
genus. All of the western moss phlox are considered to be in a separate
section from those of the East.
recent work by Carolyn Ferguson and others (Ferguson et al. 1999, 2002)
using DNA studies indicates (my interpretation) that the eastern moss
phlox are all closely
related and are relatively close to the western Subsection Nanae.
Subsections Divaricatae and Drummondianae are coherent and related, as
are the Ovatae and Paniculatae. Hybridization data (Levin 1963,
1966, and my
own observations) support these findings. I have seen no data on
genetic relationships of the western microphlox to the eastern moss
phlox, but the existence of fertile garden hybrids that appear to
involve P. subulata and western species indicate
relationships are much closer than Wherry's classification. The
forthcoming Flora of North America treatment of Phlox should give a
better rearrangement of the genus.
we are primarily interested in
phlox from a horticultural point of view, we will simplistically divide
the species into three groups based on horticultural use, which is
itself a function primarily of growth habit and also of habitat
Tall – This group is made up of the
relatively large herbaceous species, from about half a meter to over a
meter tall, most of which are found in the East, e.g. P.
paniculata, P. maculata, P. pulchra, P. ovata. These
species tend to die back to basal foliage in winter. They are used as
garden plants primarily in sunny border settings.
Medium – These average smaller and often
are semi-woody at the base. The P. pilosa-divaricata
group is included as well as the Texas annuals like P.
drummondii. P. stolonifera
and P. adsurgens, creeping plants of the woodlands
of the East and West, respectively, can go here and the western species
like the P. speciosa group and P. grayi
are probably best included. Except for the annual species, plants in
this group are usually grown as part of native habitat (e.g. woodland
or prairie) gardens. Many of the less well known species are probably
grown almost exclusively by rock gardeners, if they are cultivated at
Small – These are generally known as
moss phlox. They are semi-woody mat- or cushion-forming plants with
needle-like, more or less evergreen foliage. In the East there are
several species inhabiting sandy and rocky barrens, in the West there
are dozens of species in semi-arid and montane habitats, and in the
Arctic there are species growing in tundra. Selections and hybrids of
the eastern species (P. subulata and P.
nivalis) are commonly used as landscape plantings where a
low, dense groundcover is needed in full sun. The western species are
very difficult to grow in the eastern US; they are grown by rock
gardeners in the West and in Europe.
Phlox pages copyright 1 March 2011 Charles
WHERRY'S CLASSIFICATION OF PHLOX