Green Roofs - Living Architecture Monitor - Winter 2017 - 6

PLANT PROFILE

SEDUM:
THE WORKHORSE OF
GREEN ROOF PLANTS
BY DR. BRADLEY ROWE, MICHIGAN STATE UNIVERSITY, EAST LANSING

Since the theme of this issue of the Living Architecture Monitor is making
the business case for green roofs, I chose to write about the genera of plants
that are probably growing on more green roofs and has more to do with
driving the economic engine of extensive green roofs than any other. That is
the much maligned or much loved Sedum spp.

he genus sedum (family Crassulaceae) are a large group of
succulents that are primarily native to the northern hemisphere, but also extend into Africa and South America.
Most are found in Eurasia, but S. pulchellum and S. ternatum are both native to the eastern United States. The genus
name is derived from the Latin word sedeo meaning 'to sit' in
reference to the growing habit of many of the sedums (they sit
and sprawl over rocks). Thus the common name, stonecrop.
They are typically found in their natural habitat growing on
rocky or stony areas and do well on dry well drained gravelly
soils with limited fertility, on sunny slopes, and exhibit great
drought tolerance, especially once established. Most are herbaceous perennials and easily propagate themselves from seed or
cuttings. Prostrate stems growing along the ground often root
forming new plants. Flowers range from red to pink to yellow
to white and are known to attract butterflies. In fact, the San
Bruno elfin (Callophrys mossii bayensis), a U.S. federally listed
endangered species that inhabits rocky cliffs along the coast of
California relies on S. spathulifolium for food.
Sedum is a popular choice for extensive green roofs due
to its tolerance for drought, shallow substrate adaptability,
and ability to limit transpiration and store water. Many have
LIVING ARCHITECTURE MONITOR / WINTER 2017 / 6

been identified as exhibiting some form of Crassulacean Acid
Metabolism (CAM). CAM plants limit transpirational water
loss by keeping their stomata closed during the day. They take
up CO2 during the night, store it as an organic acid, and then
use it the following day as the source for the normal photosynthetic carbon reduction cycle.
Even though sedum are widely used on green roofs, there
is much confusion surrounding the genus. Depending on
what taxonomic expert you want to listen to, there is a lot
of disagreement on the classification of many of the 'sedum'
species used in commerce. Many that are commonly used were
formerly classified in the genus sedum, but are now segregated
into other genera such as Dudlleya, Hylotelephium, Phedimus,
and Rhodiola. A few examples include Hylotelephium spectabile (S.
spectabile), Hylotelephium telephioides (S. telephioides), Phedimus
hybridus (S. hybridus), Phedimus kamtschaticus (S. kamtscahticum),
Phedimus middendorffianus (S. middendorffianum), Phedimu spurius (S. spurium), Phedimus takesimensis (S. takesimensis), Rhodiola
rosea (S. rosea), and Rhodiola pachyclados (S. pachyclados).
Regardless of what taxonomists say, I don't believe that the
industry is going to start referring to Sedum kamtscaticum as
Phedimus kamtschaticus. An example is the common florist's
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Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Winter 2017