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 d

iverse, 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 F F F F F F F F F  M M M M M M M M M

Inflorescences

catkins

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 stigma often lobed bract 

Salicaceae - Willow family

Fruit type:

capsule

Seeds:

comose (w/long hairs)  Seeds dispersed by wind and water Cottonwood seeds

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 5 species; riparian or montane/subalpine 

In Montana: 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 long leaves w/vs.

short petioles catkins erect 1-8 stamens vs. many bud scales broad leaves w/ long petioles vs. catkins pendulous 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. papyrifera

(Paper Birch)

B. occidentalis

(Water 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. negundo

(Box Elder)

A. glabrum

(Rocky Mtn. Maple) 

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