Re: Morning Glory -Convolvulus arvensis and C. sepium

For Bob and Moira,

The white flowering morning glory I saw in Seattle was
definitely not the common bindweed, Convolvulus
arvensis, which I would have certainly recognized; as
it is also a common weed here in the SF Bay Area, but
not nearly as difficult to get rid of as some of the
others we have here. Since I didn't give a good
description of the size of the flower and plant habit,
I can understand the confusion I may have created.  I
woud have thought that the reference to full bloom in
dense shade would have ruled out Common Bindweed, as
iot does not flower successfully in shaded conditions
here, and tends to die out if it does not remain in
sun.  The vine I was asking about, and has been
tentatively identified by Diane as Convolvulus sepium,
is a much larger growing vine with larger leaves and
flowers which are also much larger, about 3 to 4" in
diameter, pure white in color, and on a vigorous vine
with deep green leaves and thick stems more similar in
appearance to the common Blue Dawn Morning
Glory/Ipomoea acuminata.  It was also equally at home
in full sun or shade, blooming in both exposures. I.
acuminata can also be a weed here in California,
especially in milder coastal areas where it is not
killed back to the ground by frost.

I would never advocate planting of common bindweed,
although some of the California native Calystegia's
are being offered for sale by wholesale nurseries
here, such as C. macrostegia var. cyclo. 'Vicente'. 
This is described as  having pink flowers marked
white, in size the flowers are similar to bindweed,
but the plant is more vining and can climb to 6 feet
tall with support.  I haven't grown this one myself,
but would assume that it is not as invasive as C.
arvensis, or I doubt it would be offered for sale.

The White Morning Glory I found interesting in
Seattle; C. sepium?, was the one I was asking about
with regard to seeding around or rooting from stems in
contact with the ground.  It was apparent that it is
wide spreading and can be a nuisance from that
standpoint, but I didn't know if it was also invasive
in the sense that it could spread into other areas by
seed or self rooting as well, which would make it
troublesome even in climates where it is not as well
adapted as in Seattle.  The ornamental Ipomoea
acuminata can and does root from stems in contact with
moist soil, and yet is still useful as an ornamental
in locations where it won't get away or overwhelm
adjacent plantings.  I. acuminata does not seem to
self seed here in our local climate, but can become a
pest in hot and humid summer climates such as the
American deep south or along the east coast.

This whole issue of weedy ornamentals which might
become escaped exotics in other areas is becoming more
important all the time.  I notice that the current
Heronswood mail order catalogue limits some plants to
local sales only, and will no longer ship certain
items to warmer, milder areas like Florida or Hawaii. 
As one example, many of the Polygonum species and
Persicaria species which were previously available are
no longer being sold by them, such as P. campanulata
and P. polystachium.  The P. campanulata does exhibit
a certain rank vigor in my own garden, but is
incapable of growing into non irrigated areas, and has
never come up from seed in other parts of the garden. 
I would suspect that Convolvulus sepium might be a
similar case, but was hoping to find out what its
exact liabilities were in the Seattle climate.  It
might be an invasive unwanted plant if grown in an
adjoining neighbor's garden, but could also be very
useful as a tough non irrigated flowering vine for a
freeway divider or to screen a junkyard, as an
example.  If the plant doesn't have the ability to
spread into other areas, it might still be useful in
certain applications.  

I hope I haven't offended anyone with my defense of
potentially weedy exotics, but with proper vigilance,
I do think that plants that are already here can be
managed to avoid invasion into natural areas, if one
knows what to look out for.  High on the list of
exotic plants to avoid are any that set viable seed
which can be readily spread, whether by birds/animals
or the winds, and in addition can survive and
reproduce without supplemental irrigation in California.

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