Lab 14: Gentians, Milkweeds, and Nightshades


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111. Apocynaceae (the part that includes the milkweeds of the former Asclepiadaceae), the milkweed and dogbane family
Diagnostic family characters
Leaves: Simple, entire, opposite or whorled, decussate.
Laticifers: Present in most species (exude a white latex when plant is broken).
Flowers: 5-merous, with androecium and gynoecium fused to form a gynostegium, pollen sacs fused to form pollinia, and a corona. Refer to the diagrams below.
Fruits: Follicles, dehiscent along the adaxial suture and filled with seeds that each have a tuft of long, silky hairs (a coma). See demonstration at front table.
Habit: Erect herbs in our flora, plus one invasive vine (Vincetoxicum).

Key out species 111: Asclepias syriaca

112. Rubiaceae, the Coffee family
Diagnostic family characters
Leaves: Opposite or whorled and generally very small (at least in temperate regions), some evergreen.
Flowers: Generally perfect, 4-merous
Fruits: Capsules or schizocarps, generally splitting into two segments.
Habit: Shrubs, or herbs (many of our herbs trailing)

In Wisconsin, an herb with opposite leaves and tiny, 4-merous flowers is most likely to be in the Rubiaceae. Two Wisconsin genera in the family do not fit this category: Cephalanthus (buttonbush) and Mitchella (partridgeberry). Five genera you are likely to run into in Wisconsin (you don't have to learn these, but look at them to get a feel for the family as a whole):

I. Galium (bedstraw). By far the most diverse genus. Trailing or upright herbs. Collect these in fruit if you can G&C 1991 perhaps lean too hard on the fruits in their key, but fruits show up in almost any key to the genus.

II. Houstonia (bluets, Quaker ladies). Pretty little plants, one species found in dry, generally sandy areas, the other in wet prairies.

III. Cephalanthus (buttonbush). The only Wisconsin shrub. This is a very distinctive plant, confined largely to floodplains and small lakes in the south central and southeastern part of the state.

IV. Diodia (button-weed, poor-Joe). A locally restricted species keep your eyes open for this along the Wisconsin and Mississippi Rivers.

V. Mitchella (partridgeberry). A common, evergreen vine of forest floors, easily confused with members of the Ericaceae.

Key out species 112: Galium aparine


113. Convolvulaceae, the Morning-glory family (incuding former parasitic Cuscutaceae)
Diagnostic family characters
Leaves: Alternate, generally cordate to hastate.
Laticifers: Present, producing a milky 'sap.'
Flowers: Showy, funnel or trumpet-shaped. Corolla in most species persists only a day before wilting.
Fruits: 4-valved, septifragal capsule (i.e. splitting longitudinally, valves breaking away from the septa)
Habit: Trailing vines

This is our most prominent family of herbaceous, twining vines. A few species in Polygonum (e.g. P. scandens, P. convolvulus) have a similar habit and leaf shape, but are distinguishable by their ocrea.

Key out species 113: Convolvulus arvensis


114. Gentianella quinquefolia 'Stiff gentian' (Gentianaceae)
This pretty little plant (6-30 inches, 3/4 inch purple flowers) is found in wet fields and rich woods. It is considered to be Appalachian in origin and in some states where it reaches the northern limits of its range it is considered endangered (although not in Wisconsin, where it is found primarily in southern prairies).

Gentianopsis crinita 'Fringed gentian' (Gentianaceae)
Note the fringed corolla of this genus. The species is considered to be endangered in some states in which it occurs. Generic circumscription in this family has changed over time; you may find this and the previous species in Gentiana, Gentianella, or Gentianopsis, depending on what source you are reading.

116. Apocynum androsaemifolium 'Spreading dogbane' (Apocynaceae)
This family resembles Asclepiadaceae in many aspects; most members have milky juice and opposite leaves, and most have a corona. You should find a host of features that help you to distinguish them. The leaves of this species are dark green above and paler and downy beneath. The flowers are white, tinged with red. Native Americans used the genus for a variety of purposes such as making rope from the epidermis and medicinal extracts from the roots to cure rheumatism, syphilis, scrofula, and heart disease.


117. Cuscuta 'Dodder' (Convolvulaceae, former Cuscutaceae)
This species and its kin are often found twined around the stems of wetland plants. They are structural parasite and nutritional (physiological) parasites and now known to be derived from more typical green, twiners of Convolvulaceae. Make sure that you are looking at the correct plant on each specimen; dodder will be the gnarly little yellow or brown thing.

Solanum 'nightshade,' 'horse-nettle' (Solanaceae)
This family contains tomatoes, potatoes, peppers, tobacco, and a really toxic chemical that can kill! The genus is recognizable vegetatively by habit (herb, often twining) and leaf morphology (notice the flanges that develop at the base of the leaves in most species). It is also distinctive florally, with petals spreading or reflexed and anthers prominent at the tip of the flower. The berries are very juicy, resembling small tomatoes, but do not eat them...

Lithospermum 'Puccoon, gromwell' (Boraginaceae)
This early prairie bloomer blooms before taller species around it reach their peak growth and crowd out its characteristic showy flowers. Unlike most members of this family the literature claims that Lithospermum is seldom pungently hairy. Nevertheless, you will find hairs on some of the species, albeit not as pronounced as in others where the hairs are dense and even prickly.

Hydrophyllum 'Waterleaf' (Boraginaceae, former Hydrophyllaceae)
The leaves of this spring ephemeral species are distinct in a number of ways. The spotted pattern looks like little drops of water on the surface of the leaf, hence the genus and common name. The flowers sport blue to purple bell-shaped corollas with the stamens being noticeably exerted. This creature should be in flower during finals, so keep an eye out for it.