100 THE MICHIGAN BOTANIST Vol. 51 RELIC OR RECRUIT? NEWLY DISCOVERED ARONIA ARBUTIFOLIA (ELL.) PERS. (RED CHOKEBERRY) IN KENT COUNTY RAISES QUESTIONS REGARDING PAST AND FUTURE DISTRIBUTIONS Michael P. Ryskamp and David P. Warners Department of Biology Calvin College Grand Rapids, MI 49546 ABSTRACT The nomenclatural history of the genus Aronia is replete with name changes, misidentifications, and debates regarding classification. In Michigan, collections of Aronia arbutifolia (Ell.) Pers. (Red chokeberry) from the early 20 th century are thought to be misidentifications of Aronia prunifolia (Marsh.) Rehder (Purple chokeberry). A recent discovery of A. arbutifolia in West Michigan could represent a rare species that has naturally occurred in Michigan in the past or an adventive individ - ual that has only recently arrived. We provide documentation of the new state record and discuss its discovery in the context of earlier ambiguous records of Red chokeberry in the Great Lakes region. We also consider whether this species is exhibiting a coastal plain disjunct distribution, and we ex - amine the possibility that Red chokeberry is expanding its range in response to climate change. Fu - ture genetic research and molecular analysis could help answer some of the questions raised by this interesting discovery in Michigan. Keywords: Red chokeberry; Aronia arbutifolia, coastal plain disjunct, climate change INTRODUCTION In 1933, at the annual meeting of the Torrey Botanical Society, renowned botanist and landscape architect Henry Teuscher (1933) gave an address on the question “ what is a species ?” In his short talk, he used the Aronia (chokeberry) complex to illustrate some of the inherent problems of using morphological cri - teria to define species of plants. Four decades later, Professor James Hardin (1973) revisited “the enigmatic chokeberries” in a paper that outlined the taxo - nomic and nomenclatural confusion surrounding the shrubs since the early 20 th century . Today, the taxonomy of the two (or three) polymorphic chokeberry species in the Aronia genus (or sub-genus) is still debated, its history likely clouded by interbreeding (Hardin 1973; Voss 1985; Voss and Reznicek 2012), different reproductive strategies (Campbell et al. 1991; Hovmolm 2004), and inter-population variability (Hardin 1973; Uttal 1984; Brand 2010). Over the years, several different genus names have been assigned to this small group, in - cluding Mespillus L., Pyrus L. f. , Crataegus Lam., Adenorachis Nieuwl., and Photinia K.R. Robertson & J.B. Phipps (MacMillin 1892; Nieuwland 1915; Brit - ton and Brown 1970) [In this paper, we follow the nomenclature outlined by Voss (1985)]. More recently, studies involving nucleotide sequencing have es - tablished molecular phylogenies of Pyrinae (Rosaceae ) that distinguish Aronia 2012 THE MICHIGAN BOTANIST 101 from Photinia (Campbell et al. 2007; Potter et al. 2007; Guo 2011). Campbell et al . (2007) recommend maintaining Photinia and Aronia as separate genera, as their results yielded no molecular evidence for placing them together, “or even near one another,” on a phylogenetic tree. The state of Michigan is no stranger to the botanical confusion associated with these shrubs. Early plant surveys in the state, circa 1900, reported Aronia arbutifolia (Ell.) Pers. (Red chokeberry) in St Clair (Dodge 1900), Berrien (Beal 1904; Hebert 1934), Ionia (Beal 1904), Kent (Cole 1901), and other counties. Botanical literature from that period, e .g., W. J. Beal’s Michigan Flora (1904) , lists two species of Aronia, A. arbutifolia and A. melanocarpa (Michx.) Elliot. (Black chokeberry) [the latter actually listed as A. nigra in Beal (1904)]. How - ever, these early records of Red chokeberry in Michigan are universally inter - preted as either reports or misidentifications of A. prunifolia (Marsh.) Rehder (Purple chokeberry) (which sometimes appeared in older literature as a variety of A. arbutifolia ). This taxon ( A. prunifolia) is typically understood to have orig - inated as a hybrid between A. melanocarpa and A. arbutifolia (Farwell 1918; Hardin 1973; Voss 1985). Our recent finding of A. arbutifolia in Kent County clarifies the occurrence of Aronia in Michigan by providing the first confirmed report of this taxon in the state. In this paper, we describe the A. arbutifolia dis - covery and then investigate some possible scenarios to explain its presence in West Michigan. MATERIALS AND METHODS On November 4, 2011, a group of eight potentially clonal Red chokeberries was discovered dur - ing a field trip to Townsend Park, Kent County, MI. The shrubs were found in a moist bottomland east of Bear Creek, growing in a backwater corridor that ran along the bottom of a west-facing hill - side. A small grove of large Thuja occidentalis (Northern White cedar) (10 –18 ′′ dbh) filled the canopy around the chokeberries, affording a relatively open understory characterized by groundwa - ter upwelling and several waste deep pockets of muck. To the west, a shrub zone of Cornus spp. (Dogwood) , Betula pumila (Bog birch) , Zanthoxylum americanum (Prickly ash) , and Physocarpus opulifolius (Ninebark) transitioned into an open wet meadow dominated by Carex stricta (Tussock sedge) , Onoclea sensibilis (Sensitive fern) , and Cirsium muticum (Swamp thistle). A shrubby ripar - ian zone marked the western edge of the meadow, the eastern banks of Bear Creek. At the time of the discovery in early November, dozens of bright-red cymose infructescences populated the distal ends of the shrubs’ branches. Tomentose beneath, the scarlet-colored leaves were elliptical and had short acuminate tips (Figure 1). The tallest shrub reached six meters in height and was supported by a cedar trunk. All the shrubs were elongate, their lower reaches mostly un- branched. Collections of flowering material were made on May 8 2012. VOUCHER SPECIMENS: Michigan, Kent Co., Cannon Twp. Townsend Park, c. 200 m SE of Ramsdell Dr. and Six Mile Rd., 43° 03 ′N, 85° 27 ′ W, 4 Nov. 2011, M.P. Ryskamp 1 (CALVIN, MICH); M.P. Ryskamp 2 (CALVIN, NY); 8 May 2012, M.P. Ryskamp 5 (CALVIN, MICH). RESULTS AND DISCUSSION The presence of Red chokeberry in Kent County raises a variety of questions with regard to the origin, establishment, and mechanism of dispersal to West 102 THE MICHIGAN BOTANIST Vol. 51 FIGURE 1. Photograph taken November 4, 2011 at Townsend Park in Kent County, Michigan showing the tomentose leaves and hairy stems of Aronia arbutifolia, with canescent berries still at - tached. Michigan. Below, we explore several different possibilities that might account for this surprising discovery, we discuss some of the implications of these possi - bilities, and we propose some future research initiatives. Given the history of misidentifications of Red chokeberry in Michigan (and in other states), one possible explanation is that what we have identified as Aro - nia arbutifolia is actually an introgressant of the hybrid ‘ A. prunifolia complex’ (Uttal 1984). This possibility, however, can be eliminated due to several distinct morphological features of the Townsend Park chokeberries. Firstly, the red- colored fruits observed on the shrubs at the time of discovery are unique to A. ar - butifolia, the fruits of A. prunifolia having a much darker purple to purple-black hue when ripe (Gleason and Cronquist 1963; Hardin 1973; Voss 1985). Uttal (1984) calls fruit color “the only reliable basis for separating chokeberry species.” The fact that both leaves and berries remained on the shrub in Novem - ber is also indicative of A. arbutifolia ; both Purple and Black chokeberry pro - duce fruit that ripen and drop earlier in the season (Hardin 1973; Voss 1985; Brand 2010). Additionally, the size of the pomes, which we measured to range 4–7 mm in diameter, is congruent with descriptions of A. arbutifolia —the pomes of A. prunifolia , in contrast, range from 8 to 10 mm (Gleason 1958; Gleason and Cronquist 1963). Lastly, Robinson and Fernald (1908) describe Red chokeberry as having cymes that are “more numerously fruited (9 –18)” than those of A. prunifolia , which have 3 –10 fruits. Even as late as November, the Townsend Park shrubs had some cymes with 10 or more pomes still attached (Figure 2), and during a field trip in May 2012, with the shrubs in full bloom, we counted 10–16 florets per cyme (Figure 3). In light of all these traits [and with confirma - 2012 THE MICHIGAN BOTANIST 103 FIGURE 2. Another photograph taken on November 4, 2011 showing the bright red fall foliage and pomes of Aronia arbutifolia . tion from A.A. Reznicek (personal observation)], we are confident that the shrubs in question are indeed A. arbutifolia. A second possible explanation for the presence of these shrubs is that they represent an escaped horticultural form. Again, we think this possibility is un - likely in light of how closely the shrubs match morphological descriptions of wildtype Aronia arbutifolia (as described in the above paragraphs). The most commonly sold cultivar (and perhaps the only one), A. arbutifolia ‘Brilliantis - sima ,’ has a more compact form, more lustrous leaves, and has larger, glossier fruits than the wildtype species (Flint 1997; Dirr 2011). This description signifi - cantly contrasts with the small canescent berries and the tall elongate growth habit of the Townsend Park shrubs. Additionally, the habitat immediately sur - rounding the Townsend Park chokeberries was replete with native species that indicate relatively pristine conditions, which differs from the typical disturbed habitat in which most non-native escapees are found (Herman et al. 2001). Though we are confident the Townsend Park shrubs are wildtype Aronia ar - butifolia, there still remain several questions regarding how, when, and from where this species arrived . Distribution patterns of coastal plain species may pro - vide important insight to these questions. There are several communities of dis - junct flora around the Great Lakes region that occur outside their primary range of the Atlantic and Gulf coastal plains (Reznicek 1994). These concentrations 104 THE MICHIGAN BOTANIST Vol. 51 FIGURE 3. Aronia arbutifolia in full bloom, Townsend Park, Kent County, Michigan, May 8, 2012.