Bulletin of the American Rock Garden Society Volume 51 Number 3 Summer 1993 Cover: Wild hybrid of Trillium erectum x flexipes, near Ann Arbor, Michigan, often mistaken for T. undulatum by Jill S. Buck of Westminster, Colorado, from photo by F. W. Case, Jr. All Material Copyright © 1993 American Rock Garden Society Bulletin of the American Rock Garden Society Volume 51 Number 3 Summer 1993 Features Trillium erectum and Its Hybrids, by Frederick W. Case, Jr. & Roberta Case 163 Vegetative Propagation in Trillium chloropetalum, by Margery Edgren 169 Waves of Bloom, by Panayoti Kelaidis 173 Plant Gems of the Austrian National Park, by Franz Hadacek 181 Plant Hunting in the USA, by Alexej Borkovec 185 American Alpines for Show, by Graham Nicholls 189 A Commitment to Fertility, by Gwen Kelaidis 193 Bulletin Editors since 1962, by Mamie Flook, with Buffy Parker 205 Sedums as Foliage Plants, by Ladislav Hlavaty 215 Departments Seed Exchange 219 Propagation 225 Trillium flexipes 162 Bulletin of the American Rock Garden Society Vol. 51(3) Trillium erectum and Its Hybrids by Frederick W. Case, Jr. & Roberta Case- Until 1962, no one, to my p. 199). Our field work established that knowledge, had reported the existence the Farwell forms grew mostly where of hybrids in the genus Trillium. At stream flood plains interlaced with acid that time, George Burrows and we uplands, bringing the two species close postulated the existence of wild hybrids enough together that bees could cross- based upon occurrence of peculiar trilli- pollinate them. We concluded that ums in southeastern Michigan. Botanist these "forms" were actually hybrids, 0. A. Farwell had described several and that some of the darker and more "forms" of the local but widespread unusual forms were backcrosses. Trillium flexipes Raf. (also known by Subsequently, we have hand-pollinat• the botanically illegitimate names T. ed selected typical white-flowered declinatum [Gray] Gleason, and T. plants of T. flexipes with typical red- gleasonll Fernald). While typical T. flowered T. erectum and produced flexipes is white-flowered (photo, p. offspring with color patterns identical to 198), Farwell's forma blllingtonil has those of the putative wild hybrids, thus white petals, but each with a distinct, confirming that these beautiful forms dark reddish-brown blotch at the base, were, indeed, hybrids. superficially similar to the pattern in Not all trilliums will hybridize. Trilli• Trillium undulatum. In forma um grandiflorum, one of the showiest walpoleii Farwell, the entire petal is a and most popular species, apparently dusky buff, tan-red, or reddish color. will not cross with any of the other In mapping the distribution of the species. On the other hand, evidence species and forms for our 1962 paper, here in our garden and in our field stud• Burrows and I noticed that Farwell's ies across the southeastern United strange color forms occurred in Michi• States indicates that a large and closely gan only in those counties where the related group of trilliums whose flowers range of T. flexipes overlapped that of are all pedunculate (borne on short the wake robin, T. erectum L., a dark stems), including T. flexipes, T. erec• red-maroon-flowered species of acid tum, T. erectum ssp. sulcatum, T. upland or cedar swamp borders (photo, cernuum, T. simile, T. rugellii, and T. 163 vaseyi, may all interbreed. Most of the lands, usually in slightly acid soils. It can known hybrid populations, however, be miffy in cultivation. From a horticul• involve forms of the species T. flex• tural standpoint, T. flexipes is clearly ipes crossing with T. erectum. Fortu• the more desirable species. nately, these parents produce some fine Trillium erectum, red trillium or offspring. wake robin, has flowers typically deep maroon-red, fading to dull purple-red Trillium flexipes Raf., T. erectum L. with age. In northern races the petals and Their Hybrids are lanceolate-ovate, somewhat twisted, Trillium flexipes, a robust, peduncu• and heavy textured. The ovary is round, late trillium, occurs naturally from low-ridged, and nearly always dark Minnesota and Missouri east to south• purple-red to reddish-black. Flowers ern New York, and southward, mostly carry a faint fetid scent of wet dog. On west of the Appalachians, into Alabama maturity, the ovary remains relatively and northern Georgia. It varies consid• small and rounded, not pyramidal. erably within that range from having Leaves are rhombic. The plant naturally strongly nodding, even recurved, tends to form clumps (photo, p. 199). peduncles bearing the flowers below In northern forms, the flowers, despite the leaves to rigidly erect and outfacing the name, are rarely erect: typically, the blooms. Petals range from occasionally rather long peduncle (flower stalk) leans thin to usually heavy-textured, and from or dangles, displaying the flowers narrowly lanceolate to broadly ovate. In toward the side or the ground. Anyone most forms the color is ivory-white. doing extensive field work or visiting Some forms bear delightfully scented habitats over this species' vast range flowers, the fragrance suggesting old (uplands from Newfoundland to Geor• garden roses. Flowers last about two gia, the Cumberland Plateau, and local• weeks, long for a trillium. The ovary is ly in Ontario and Michigan) soon comes white or flecked pink and pyramidal in across color variants. In any given shape. It ripens into a reddish-pink region it is possible to find individual berry as big as a crabapple with a fruity plants with soft chartreuse-yellow, fragrance. white, or rose-pink flowers among the Trillium flexipes grows mostly on deep maroon-red ones. The color situa• neutral or slightly basic soils over lime• tion in these parents and hybrids is stone, or on stream flood plains, or at complex and produces some highly the bases of hills. Often confused with significant variations of interest to wild- the northern nodding trillium, T. flower and rock gardeners. Let's look cernuum L., T. flexipes has larger further at these plants. leaves more rhombic in shape, larger, heavier-textured flowers usually less Color in Trillium nodding, and large, yellow anthers with Coloring in flower petals is produced almost no filament stalk. Although either by cell sap pigments, vacuolar superficially similar, nodding trillium has pigments (in the vacuoles or internal thin-textured, smaller flowers, nearly storage chambers of the cell), or always recurved below the smaller discrete cell organelles termed plastids leaves, and the stamen consists of a that contain characteristic pigments. purplish anther and filament, about Exact tone of some of these pigments equal to each other in length. Nodding changes at different acidity or alkalinity trillium grows in cool soils of bogs, levels (pH) in the cell. All these factors stream banks and far northern wood• appear to be controlled by genes, and 164 Bulletin of the American Rock Garden Society Vol. 51(3) combinations of all may control color in tinguishable to our eyes, may be linked a single flower petal. To a lesser with a visible pigment in the hybrid, degree, color may be affected by envi• producing flowers with centers the dark ronmental factors, such as light intensi• color of T. erectum against white back• ty and temperature during bud grounds the color of T. flexipes development, or by soil pH. (photos, p. 202). Or if the T. erectum What we see as the maroon-red parent is itself a color form or mutant, petals of T. erectum, if we correctly then hybrids of varying tones appear. interpret what we see, is actually the We have plants with white petals and result of a series of pigment and plastid pale green centers, and others with overlays of various colors and of cell dark red centers (photo, p. 200, 203, pH, each controlled by a different gene. 204). Backcrossing to either parent or Together, these produce the deep red crossing two hybrids results in a myriad color. If deletion mutations occur, one of varied patterns and shades (photo, p. or more colors could be dropped, or 200). cell chemistry altered, resulting in the One type of hybrid, fairly common various color forms and tones occasion• here, reverses the color pattern: instead ally found. But coloring is still more of the petal base being dark, it is white, complicated. and the distal portion of the petal is Many insects see mostly reflected dark, resulting in dark flowers with a ultraviolet light wavelengths that are light bull's eye center, very dramatic largely invisible to humans. What we (photos, p. 202). see and what the insect sees are quite Some plants have produced a color different. Ultraviolet (UV) photography break similar to that of some picoteed has shown that many flowers that tuberous begonias, with the petal appear to us to be unicolored actually margins colored darkly and flecks of absorb and reflect UV light in patterns, color scattered across the face of an forming guidelines or targets visible to otherwise pale petal (photo, pp. 200, insects. These draw the pollinators into 203). The effect is dramatic and lovely critical areas of a blossom where they and does not appear to result from a may effect a transfer of pollen. Such a disease such as color break virus as in situation apparently exists in the group Rembrandt tulips, nor from mycoplas- of species related to T. erectum and T. ma organisms, as in the green and flexipes. Indeed, in one southern vari• white mottled T. grandiflorum. This ety of the red trillium, T. erectum var. picotee and another clone, a bright sulcatum (or T. sulcatum Patrick), one rose color, bear stiffly erect flowers and can often observe a faint, slightly darker possess a strong clumping habit bull's eye pattern in the center of the (photos, p.