Today’s plants (all within subclass Rosidae)
Rosid trees
Salicacaeae
Salix (willows)
Populus (aspens, cottonwoods)
Betulaceae
Betula (birches)
Alnus (alders)
“Aceraceae” (now in Sapindaceae)
Acer (maples)
Salicaceae - Willow family
Habitats
diverse, but generally high elevation or riparian
Growth habit
trees, shrubs
Leaves
alternate
simple
dentate
with stipules

Salicaceae - Willow family
Flowers
unisexual (imperfect)
species usually dioecious
may be wind-pollinated
or insect pollinated
Inflorescences
catkins
FF
F F
F
FF
F
F

M M
M
MM M
M M
M
catkin = a dense inflorescence of unisexual, apetalous flowers
Salicaceae - Willow family
Sepals
0 or many
often reduced
may be connate

Petals
0
Stamens
2 - many
(in staminate flowers only!)
Salix - male flowers
Salicaceae - Willow family
Gynoecium (in pistillate flowers only!)
syncarpous, 2 - 4 carpels
superior ovary
bract
stigma often lobed


Salicaceae - Willow family
Fruit type: capsule
Seeds: comose (w/long
hairs)
Cottonwood seeds
Seeds dispersed by wind and water

Salix - Willows
In Montana: 50 species; diverse habitats
Growth habit: few trees, many shrubs or creeping shrubs
S. arctica
S. fragilis
Salix - Willows

many species
of riparian shrubs
Often spreading vegetatively
Often hybridizing
Populus - Aspens, Cottonwoods

In Montana: 5 species; riparian or montane/subalpine
Growth habit: trees
P. tremuloides (Aspen)
P. balsamifera (Cottonwood)
Elk & Aspen
Salicaceae - Willow family
Salix
vs. Populus
mostly shrubs
vs.
mostly trees
1 bud scale
vs.
many bud scales
long leaves w/vs.
short petioles
broad leaves w/
long petioles
catkins erect
vs.
catkins pendulous
1-8 stamens
vs.
6-many stamens

Salicaceae - Willow family
Salix: 1 bud scale
Populus: > 1 bud scale
Salicaceae - Willow family
Salix
Populus
Salicaceae - Willow family
Salix (upright)
Populus (hanging)
Betulaceae - Birch family
Distribution: world-wide; primarily north temperate
In Montana: 3 genera, 6 species
Growth Habit: trees/shrubs
Leaves:
alternate, simple
serrate or doubly serrate
Genera to know:
Betula (birch)
Alnus (alder)

Betulaceae - Birch family
Inflorescences: catkins of reduced flowers
Flowers: unisexual
plants monoecious
wind-pollinated
female catkin
male catkin

Betulaceae - Birch family
Sepals
1-6
often scale-like
always distinct
Petals
0
Stamens
2-8
male flowers

Betulaceae - Birch family
Gynoecium
2 fused carpels
in dense, cone-like catkin
with bracts
Fruit types
nutlet
samara (winged nutlet)


Betula - Birches
In Montana: 3 species; often near streams/lake shores
Growth habit: trees/shrubs
B. occidentalis
(Water Birch)
B. papyrifera (Paper Birch)
Alnus - Alders
In Montana: 1-2 species; wet areas, near streams/shores

Growth habit: small trees/shrubs here (large trees in PNW)
Betulaceae - Birch family
Alnus: female catkins
woody and persistent
Betula: female catkins
not woody

Betulaceae - Birch family
Alnus: stalked buds
Betula: blistered bark

“Aceraceae” - Maple family
Now in Sapindaceae (large family of mostly tropical trees)
In Montana: 1 genus w/ 3 native species & 1 invasive
Habitat: primarily in riparian areas, open pine forest
Acer - Maples
Growth habit: trees/shrubs

Leaves:
opposite
simple, often palmately lobed
1 sp. pinnately compound
A. glabrum (Rocky Mtn. Maple)
A. negundo (Box Elder)
Acer - Maples
Inflorescences: umbels w/ long flower stalks
Flowers
unisexual & regular
trees monoecious
Sepals
4 or 5
Petals
0
Stamens
usually 8 (in staminate flowers)

Acer - Maples
Gynoecium (pistillate flowers only)
2 fused carpels => 1 ovary w/ 2 styles
ovary superior
female flowers have non-functional stamens

Acer - Maples
Fruit type
samara = winged nutlet
(in pairs => schizoid samara)

Norway Maple
A. platanoides
Ulmaceae - Elms, Hackberry
Fagaceae - Oaks, Beeches, Chestnuts
Fagaceae - Oaks, Beeches, Chestnuts