Flowering Plants: Nightshades to Mistletoe

Cuscutaceae -- Dodder Family

102 I NIGHTSHADES TO MISTLETOE ""r--+++--\ COMMON NAME: Ascending Morning-glory. HABITAT: Disturbed soil. RANGE: North Dakota to Montana, south to Arizona and Missouri; adventive in Illinois. ILLINOIS DISTRIBUTION: Kane Co.: west of Montgomery , July 4, 1976, R. Young s.n. '--'--~"' This adventive from the western United States is associated with Callirhoe involucrata and Penstemon cobaea at its Illinois location. Although Evolvulus pilosus Nutt. is sometimes used for this species, it is apparently an invalid binomial. It flowers during the summer. CUSCUTACEAE-DODDER FAMILY Twining, annual parasitic herbs, without chlorophyll, attached to hosts by means of haustoria; stems threadlike, orange or yellow; leaves scalelike, much reduced, without chlorophyll; flowers in cymes, sometimes densely crowded and resembling a head or spike, perfect, actinomorphic; calyx 4- or s-parted; corolla 4- or sparted , white, with a diversity of fringed or cleft scales on the tube beneath each stamen; stamens 4-5, alternating with the lobes of the corolla; ovary superior, 2-locular, with 2 free or united styles; fruit a capsule. Only the genus Cuscuta, with 150 species found worldwide, comprises the family. All species are noxious and harmful weeds that severely parasitize their hosts. Although Cuscuta is traditionally placed in the Convolvulaceae, I am following Cronquist (1981) in recognizing it in its own family because of its absence of chlorophyll and its anatomical and chemical differences. 1. Cuscuta L. -Dodder Parasitic annual herbs; stems twining, with minute suckers, orange or yellow or red; leaves reduced to alternate scales, or absent; flowers in cymes, perfect, actinomorphic; calyx 4- to s-parted, or the sepals free; corolla campanulate to urceolate, 4- to s-parted; stamens 4-5, free, attached to the corolla; pistil1, the ovary superior, 2-locular, with 2 ovules per locule; styles 2, usually free; capsule circumscissile, 1- to 4-seeded, the seeds glabrous. Species differentiation is often difficult, and use of a hand lens Cuscuta I 103 is usually necessary for identification. Often there are petaloid scales between the lobes of the corolla that need to be examined. Various species have been found on a wide variety of herbs and shrubs. Usually more than one kind of species can serve as host to a species of Cuscuta. The seeds of Cuscuta germinate in the soil. Upon emerging from the ground, the seedling immediately attaches itself to the host plant by means of minute suckers. Yuncker (1932) has made a thorough study of the genus. Engelmann had initiated studies on the American species as early as 1842. KEY TO THE SPECIES OF Cuscuta IN ILLINOIS 1. Sepals free to base -------------------------------------- 2 1. Sepals united below into a tube ---------------------------- 4 2. Flowers pedicellate, borne in rather loose cymes or panicles; seeds 1.4-1.5 mm long-------------------------- 1. C. cuspidata 2. Flowers sessile, borne in dense glomerules; seeds 1.7 mm long or longer _____________________________________________ 3 3· Bracts at base of sepals appressed; lobes ofcorolla obtuse; seeds 2. 5-2.6 mm long___________________________________ 2. C. compacta 3· Bracts at base of sepals with recurved tips; lobes of corolla acute; seeds 1.7-1.8 mm long ---------------------------- 3· C. glomerata 4· Most of the flowers with 4-lobed corollas------------------- 5 4· Most of the flowers with 5-lobed corollas------------------- 7 5· Corolla lobes erect; flowers sessile or on pedicels up to o. 5 mm long __ ---------------------------------------------------- 6 5· Corolla lobes inflexed; flowers on pedicels usually at least 1 mm long__ -------------------------------------------- 6. C. coryli 6. Scales absent, or reduced to minute teeth along the filaments; lobes of corolla acute, about as long as the corolla tube; seeds 1.3-1.4 mm long_________________________________ 4· C. polygonorum 6. Scales toothed from base to apex; lobes ofcorolla obtuse to subacute, shorter than the corolla tube; seeds 1.6-1.7 mm long ----------- ------------------------------------- 5· C. cephalanthi 7· Lobes of corolla obtuse, erect or spreading__________ 7· C. gronovii 7· Lobes of corolla acute, the tips inflexed ---------------------- 8 8. Lobes of calyx obtuse; pedicels shorter than the flowers ------- g 8. Lobes of calyx acute; pedicels as long as or longer than the flowers --------------------------------- 10. C. indecora g. Lobes of corolla acuminate; scales about half as long as corolla tube; seeds 1.0-1.2 mm long ---------------------- 8. C. pentagona 104 I NIGHTSHADES TO MISTLETOE g. Lobes of corolla acute; scales about as long as corolla tube; seeds 1.s1 .6 mm long_______________________________ g. C. campestris 1. Cuscuta cuspidata Engelm. Bost. Journ. Nat. Hist. 5:224. 1847. Fig...