Lab 11: Oaks, Birches, and Evening Primroses


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Introduction: During the next section of this course (leading up to exam II), the format of lab will be more advanced. The focus will be on learning characteristics of different angiosperm families, genera, and species, with comparative study of the morphology of different genera and Tricky Look-Alikes. You are responsible for all identification information presented on the handouts from here on out. Ecological information is extra and you will not be tested on it in this class, though understanding it may help you remember some of the morphological characteristics of different families and genera.
Key out the first three taxa as you have been doing, beginning at the key for the family. Also key out the fourth species from the beginning of the keys, so you stay in practice using family keys.

81. Fagaceae
Diagnostic family characters
1. Woody plants with alternate, simple leaves, toothed and pinnately veined.
2. Monoecious with staminate flowers in aments (catkins) or dense globose heads; pistillate flowers in reduced cymes.
3. Fruits are nuts subtended by an involucre: in beeches and chesnuts, the involucre is spiny and splits open to release the nut in acorns (produced by oaks), the involucres stays attached as the acorn 'cap.'

The oaks are an ecologically very important group. They can be distinguished from the other members of the family by the fact that the terminal buds form clusters at the shoot tips (see demo branches). The group is highly fire adapted, both because of the ability to resprout readily after fire and because many have thick bark that protects the plant from the heat of a fire. Take a look at the corky branches of bur oak (Quercus macrocarpa) in comparison to the thinner bark of black-Hill's oak (Q. ellipsoidalis x velutina). Bur oak survives fires by perservering. Black and Hill's oak survive fires by resprouting.
Also look at the thicker trunk bark of black oak (Q. velutina) relative to that of white oak (Q. alba). White oaks do not generally grow out in open savannas, as their close relatives bur oaks do. The bark in the white oaks is forced to flake off by a fungus (Aleurodiscus oakesii) that is much more common in woodlands than in open areas.
There are two subgenera, the white oak group and the red / black oak group:

 White oak group
(subgenus Lepidobalanus)
Leaves. Not bristle-tipped
Fruits. Mature within one season
Stigmas. Sessile or nearly so
Abortive ovules at base of seed

 Red oak group
(subgenus Erythrobalanus)
Leaves. Lobes bristle-tipped
Fruits. Mature in the second season
Stigmas. On elongate styles
Abortive ovules at the top of the seed

Key out: Quercus macrocarpa 'Bur oak'
Genera for comparison: Quercus, Fagus, Castanea

82. Betulaceae
Diagnostic family characters
1. Woody plants with alternate, simple leaves, toothed and pinnately veined.
2. Monoecious with all flowers in aments (catkins).
3. Fruits are tiny or medium sized nuts, nutlets, winged or unwinged (if winged then called samaras).

Many of these species are fast-growing and early successional, while others are found as understory trees in mature forests. The bark often has prominent lenticels. Look at the paper birch bark to see these. Also look at the European alder (Alnus glutinosa) 'cones.' Unlike the Fagaceae, Betulaceae have both staminate and pistillate catkins. European alder can be found in wetlands all over town. It is a pretty noxious weed.

Key out: Betula papyrifera 'Paper birch'
Genera for comparison: Betula, Alnus (shrubs), Corylus (shrubs), Carpinus, Ostrya

83. Lythraceae
Diagnostic family characters
1. Herbaceous plants with leaves opposite or whorled, entire-margined
2. Perfect flowers, perigynous, with a well-developed hypanthium, stamens with unequal filaments inserted on inner surface of the hypanthium below petals
3. Fruits are dehiscent capsules enclosed in the persistent hypanthium; rarely berries.

Key out to genus only: Lythrum
Genera for comparison: Lythrum, Decodon, Rotala, Ammania, Didiplis

Plant to key out (and learn):

84. Oenothera biennis complex (Onagraceae) 'Common evening primrose'

Formula: CA4 CO4 A8 G4 (inferior ovary, fused carpels). This herbaceous bienniel takes two years to complete its life cycle. Look for this species in more xeric sites, like prairies savannas, and roadsides. Like other members of the Onagraceae, Oenothera biennis is nicely 4-merous, with an inferior ovary and a relatively long hypanthium tube. The Greek translation of Oenothera, literally means “to imbibe in wine”, as it resembles a plant thought to increase one’s thirst for wine.

Species to learn:
85. Ostrya virginiana (Betulaceae) 'Eastern hophornbeam
' 'ironwood'
This common understory shrub or small tree is common across the state of Wisconsin. The male and female catkins live in the same house (monoecious); the tiny flowers open mid-spring. The nuts are associated with pale green bracts, clustered together on “cones”, hence the common name hophornbeam. There are a number of tree species that look very similar to this (and even have similar common names) so use your resources to help identify this species.

86. Staphylea trifolia (Staphyleaceae) 'Bladder- nut'
This native shrub is the only species of Staphylea, and Staphylea the only genus from Staphyleaceae, that you will find in WI. The leaflets of the trifoliolate compound leaves are mounted on the end of rather long petioles. The bell-shaped, greenish-white flowers are also found at the end of long pedicels. The bark is stripped. Native Americans apparently used parts of this plant to relieve constipation.

Genera to learn:
87. Geranium (Geraniaceae) 'Geranium'
This genus is quite popular as a house plant, nevertheless there are several different species of Geranium that you are likely to come across in the field. They commonly have palmately or pinnately compound leaves and many are covered head to toe with glandular hairs containing ethereal oils. They usually have brightly colored flowers (blues and reds) and nectar-producing glands.

88. Oxalis (Oxalidaceae) 'Wood-sorrel'
All of the Oxalis spp that you might encounter in WI have palmately compound trifoliolate leaves originating from basal rosettes. Several of them have pulvini at the bases of the petiolules which cause the leaflets to fold down and appear to go to sleep. They commonly contain oxalic acid and therefore make a tart little snack. Do not confuse them with the other 'sorrel' that we learned (Rumex), also tart to the taste.

89. Epilobium (Onagraceae) 'Willow-herb'
This genus is native to most of the temperate regions of the world. It is 4-merous. Epilobium species have a hypanthium that varies from short to elongate from species to species. Epilobium angustifolium, 'Fireweed,' is abundant in WI. It is an early colonizer after fires but is also found in waste places and roadsides.

90. Carya (Juglandaceae) 'Hickory'
Hickories have pinnately compound leaves and imperfect flowers in spicate inflorescences. The carpellate (female) inflorescences are erect and the staminate (male) ones are pendulous. You are probably familiar with the leathery drupe-like nut with a single massive seed found inside. The seed coat, as well as other parts of the plant, contains relatively high concentrations of allelopathic (inhibiting to other plants) compounds.