Lab 12: Mustards, Mallows, and Maples


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91. Brassicaceae
Diagnostic family characters
Leaves simple, sometimes pinnately lobed (see the basal leaves on the Bursa plant at your table)
Flowers 4-merous with 2+4 stamens (tetradynamous). The old family name Cruciferae refers to the cross-shaped flowers.
Fruits generally siliques or silicles, though berries and capsules are also found in the family
Glucosinolates (the acrid juice that gives kale, cabbage

The fruits form from a 2-locular ovary with parietal placentation and have a distinctive morphology:
the replum is the margin to which the ovules attach and encircles the edge of the fruit
the septum is the false partition (it is referred to by some as a false septum, though keys probably will not describe it as false it is actually formed by outgrowths of the placentae)

Two typical fruit types:
Silique: ca. 2-3 times longer than broad.
Silicle: wider than long or about as wide as long.

Key out species 91: Hesperis matronalis 'Dame's rocket' CA CO A G


92. Sapindaceae, the Maple family. Note: the former Aceraceae (maples only) and Hippocastanaceae (buckeyes only) are placed now within the mostly tropical family Sapindaceae.
Diagnostic family characters
Woody plants, generally trees or shrubs
Leaves opposite, palmately lobed or veined in some species, trifoliolate or pinnately compound
Flowers small, commonly with intrastaminal nectary disk
Fruits generally double samaras (winged achenes)

The family is monogeneric in the state. Species within that genus may be divided into two morphological groups based on whether the sinuses of their leaves are sharply-angled or rounded. See the demonstration of what this distinction looks like.
Samara morphology is sufficient to distinguish species, but most people do not learn the characteristics.

Key out species 92: Acer negundo 'Box-elder,' 'Ash-leaved maple' CA CO A G
[Are these flowers male or female?]

93 & 94. Anacardiaceae, the Cashew, Sumac, and Poison Ivy family
Diagnostic family characters
Woody plants with well-developed resin canals in the bark; resin in many species causes dermatitis
Leaves usually alternate, pinnately compound
Flowers unisexual, plants usually dioecious
Fruits small, berry-like drupes (typically white or yellowish in one genus)

Key out species 93: Rhus glabra 'Smooth sumac' CA CO A G
[An additional species, R. hirta, provided for comparison only.]
In this genus, the fruits are glandular-pubescent and red. The fruits can be steeped in cold water and the resulting drink sweetened to make a tasty lemonade-like tea. The resins in this genus are not toxic.

Key out species 94: Toxicodendron radicans 'Poison ivy'
[An additional species, T. vernix, provided for comparison only.]
In this genus, fruits are glabrous and greenish to white. Resins are toxic.
Some people may not be allergic to poison ivy but additional exposure may sensitize them. Therefore, even if you are not allergic it is a good idea to avoid this plant in order to stay that way. In some older literature you may see this species referred to by a variety of different names.


Species to learn:

95. Acer saccharum (Sapindaceae, former Aceraceae) 'Sugar maple'
The sugar maple is ubiquitous in southern Wisconsin forests; look for basswood (#96) growing in the same forests. There are a number of species of maple native to Wisconsin forests, however none are as economically important as this species. It is exactly this time of year when the juices begin to flow in the sugar maple, inspiring many to collect gallons of the sap and boil it down to sweet maple syrup. Where would pancakes and waffles be without the sugar maple?

96. Tilia americana (Malvaceae, former Tiliaceae) 'Basswood' 'Linden'
This native species is common in mesic forests throughout the state. The inner bark may be spun into strong twine. The species planted as street trees around the city are Eurasian (T. platyphyllos and T. cordata). They have significantly smaller leaves. All species in this genus have a unique bract subtending the inflorescences (see the "Small-leaved Linden" poster above the computer). Tiliaceae, and two other primarily tropical families including cola and chocolate, are now included in the mallow family.

Genera to learn:

97. Alliaria (Brassicaceae) 'Garlic mustard'
Alliaria petiolata is one of our most obnoxious weeds of dry to mesic woodlands. The species is biennial and sits as a rosette of leaves the first year before flowering in the spring of the second year when each plant releases thousands of tiny seeds.

98. Cardamine (Brassicaceae) 'Toothwort, Cuckoo flower, Spring cress'
The genus includes a number of early spring flowering herbs of woodlands and open areas. The toothworts include common herbs seen in woodlands at the 401 exam time. As the name implies, the toothworts (but not all species) have toothed and/or lobed leaves.

99. Zanthoxylum (Rutaceae) 'Prickly-ash'
Although native, this prickly stemmed clonal bush is becoming invasive in prairies and wood edges. Leaves are pinnately compound and have oils of reputed medicinal value. The inflorescence appears before the leaves.

100. Malva (Malvaceae) 'Mallow'
It appears to be that all of the Malva species found in WI are non-native. This group may be confused with Geranium given that their leaves look alike and both are covered with hairs. The stamen-column bearing anthers at the summit is one feature that can be used to tell them apart. So is the pubescence: Malvaceae possess very distinctive stellate hairs that show up readily under a hand lens.
Look at the dried infructescence (from a close relative) to see why another common name for some Malva species is 'cheeses.' Some close relatives are Gossypium, 'cotton,' and Hibiscus, an ornamental with which you may be familiar.