Introduction

Oeceoclades maculata (Lindl.) Lindl. (= Eulophia maculata (Lindl.) Rchb.f.) (Orchidaceae) has a broad native range across tropical Africa and Madagascar (^{Stern 1988}). In addition, this species has become widely naturalized in the New World. Oeceoclades maculata is commonly known as the monk orchid or the African spotted orchid. The specific epithet, maculatum, means ''spotted'' in Latin, relating to the distinctive mottling on its leaves (Fig. 1).

(a). Bud with a distinct spur.

(b). Back of the mature flower.

(c). Front view of a mature flower.

Figure 1 Oeceoclades maculata illustrated by Sarah K. Wetterer. 

The full plant body of O. maculata has one or more pseudobulbs, each with a single leaf or leaf remnant at the top (Fig. 1). Each pseudobulb develops surrounded by a fibrous sheath that can wear off over time. The central ridge of the leaf, which allows O. maculata to be easily distinguished from Dracaena trifasciata (Prain) Mabb. (= Sansevieria trifasciata), is clearly visible. The flower stalks grow from the base of the pseudobulb and the flowers mature sequentially. The dehiscent seed capsule is pendant and heavily ridged. The stamens, style, and stigma are all combined into the central column and with an anther cap that covers the pollinarium. When disturbed the cap comes free, thus allowing for self-pollination (^{González-Díaz & Ackerman 1988}).

Oeceoclades maculata has many qualities that allow it to readily colonize new areas. In addition to having small, wind dispersed seeds, it is autogamous (self-pollinating), capable of vegetative reproduction, and has a wide ecological amplitude. This means that it can successfully colonize many habitats and can found a viable new population from a single individual. Under proper conditions, O. maculata can grow from seed to flowering in a single year (^{Adamowski 1999}).

John Lindley (1799-1865), an English botanist, described Angraecum maculatum (=Oeceoclades maculata) based on a cultivated greenhouse specimen sent to him by George Loddiges & Sons, the owners of the Hackney Botanic Nursery, located in Hackney, north of London, England. ^{Lindley (1821}) wrote ''Messrs. Loddiges inform us that they are uncertain from what quarter they received it, but they think from South America.'' (Many references incorrectly state that Lindley described O. maculata based on a specimen known to be from Brazil.) Later the same year, ^{Link and Otto (1821}) described the same species, also from a cultivated specimen, as Geodorum pictum Link & Otto (= O. maculata).

The earliest known record of O. maculata, however, is at least 30 years older, made by José Mariano de Conceição Vellozo (1742-1811), a Brazilian botanist who illustrated and described Epidendrum connivens Vellozo (= O. maculata), based on a specimen from ''S. Crucis'' (Santa Cruz, Brazil). In 1790, Vellozo brought his manuscript describing 1,640 Brazilian plant species to Lisbon for publication, but these descriptions were not published until long after his death (E. connivens illustration in 1831, description text in 1881). All subsequent records of O. maculata in the New World come from South America, until one was recorded from Trinidad in 1962 (Tables 1 - 3), which is the first known record outside of the South American continent.

In 1974, Robert Grimm, a professor of botany at the University of Miami, discovered the first North American population of O. maculata while he was leading a group of students on a fieldtrip to Matheson Hammock Park, Miami-Dade County, Florida (^{Hammer 2001}). ^{Hammer (2001: 77)} wrote: ''It has been reported that O. maculata originally escaped into Miami-Dade County's Matheson Hammock from Fairchild Tropical Garden, but a check by the author in 1974 revealed that this species has never been accessioned at the Garden and none of the staff ever recall propagating it there. By whatever means it arrived in Florida, it is certainly here to stay.

^{Hammer (2001: 76)} reported: ''This rapidly dispersing orchid has since invaded natural habitats and disturbed sites throughout South Florida and much of Central Florida and is expected to continue its advance northward. It has already moved as far north as Brevard and Sarasota counties. University of Florida professor, William L. Stern, collected plants in MiamiDade County to study, and those that he cultivated at Gainesville (Alachua County) escaped cultivation and managed to survive several winters before succumbing to a prolonged hard freeze.''

The present study was motivated by our discovery of a large population of O. maculata in a reserve near our home in South Florida. We were particularly interested in documenting the spread of this orchid north, into more subtropical parts of the state. Here, we document the continued spread of O. maculata in the New World, using published records, herbarium specimens, photographs posted online, and our own collections. Oeceoclades maculata is relatively easy to identify both in the field and in photographs. It has a superficial resemblance to the snake plant, Dracaena trifasciata, another plant native to Africa that is spreading in the New World. While both O. maculata and D. trifasciata bear leaves mottled with different shades of green, O. maculata can be distinguished by its prominent midvein, pseudobulb, and smooth, rounded leaf edge (Fig. 1). In contrast, D. trifasciata lacks a midvein and pseudobulb and has ridged leaves with curved margins that come to a sharp point.

Materials and methods

We compiled O. maculata site records from many online sources, including Atlas of Florida plants (^{Wunderlin et al. 2021}), EDDmapS (^{EDDmapS 2022}), iDigBio (^{iDigBio.org, 2022}), The Floristic Inventory of South Florida (FISF; ^{Gann et al. 2022}), and Tropicos (^{tropicos.org, 2022}). We also obtained site records of O. maculata based on photographs posted online at several sites, including ^iNaturalist (iNaturalist.org), Flickr (Flickr.com), and Project Noah (projectnoah.org). These photographs proved to be a very useful source of site records. Oeceoclades maculata is an attractive plant that is frequently photographed and is simple to distinguish in photographs from other species from the New World. SKW confirmed the identification of each photographed specimen posted online. We did not include records based on photos that were too blurry or showed only the capsules, which lack characters distinct enough to allow positive identification. A few photos posted online as O. maculata were misidentified as D. trifasciata and vice versa. We did not map records of O. maculata in cultivation or photographed in flowerpots or gardens.

We obtained geographic coordinates for collection sites from published references, specimen labels, maps, or geography websites (e.g., Google Earth (earth.google.com), Tageo (www.tageo.com), and Falling Rain (www.fallingrain.com)). If a site record listed a geographic region rather than a ''point locale,'' and we had no other record for this region, we used the coordinates of the largest town within the region or, in the case of small islands and natural areas, the center of the region. Some early records of O. maculata lacked important site data, often listing only the country or province, or giving an ambiguous locale name, but we mapped the record to the most likely locale. For example, ^{Vellozo (1881}) painted and described Epidendrum connivens (= O. maculata) from Santa Cruz, Brazil sometime before 1790. Although there are now many towns named Santa Cruz in Brazil, we mapped this record to Santa Cruz, Minas Gerais because Vellozo was from a town in Minas Gerais only 7 km east. In May 1841, Scottish naturalist George Gardner collected O. maculata specimens in the state of Maranhão, Brazil. Although no additional site data was recorded, ^{Gardner (1846)} wrote that during his three weeks in Maranhão in May 1841, he was only able to visit the area around the port of São Luis and nearby Alcantara due to rain. ^{Hauman (1917}) described Eulophidium maculatum pterocarpum from a specimen reportedly collected in 1900 at the mouth of Rio Pilayá, a tributary to the Rio Pilcomayo. Although ^{Hauman (1917}) listed this site in Formosa Province, Argentina, we mapped this record to the actual location of the mouth of the Rio Pilayá, which is in Bolivia, ~300 km NW of the nearest point in Formosa Province, Argentina.

We divided records of O. maculata into four time periods and mapped them using different colors: Red = 1790-1900, Orange = 1901-1960, Green = 1961-1990, Blue = 1991-2021. If the earliest record we found for a country lacked specific site information and we had no other records of the same period, we mapped the data point to the largest city: French Guiana (Cayenne), Guyana (Georgetown), and Venezuela (Caracas).

Records usually included collection dates, but in several cases, publications did not include the collection dates for specimens. For many of these records, we were able to determine the date based on information on the collector's travel dates or limit the date by the collector's date of death.

Results

We compiled several thousand records of O. maculata from the following geographic areas in the New World: 11 South American countries (all except Chile and Uruguay), all 7 Central American countries, Mexico, 23 West Indian island-groups, and Florida (Tables 1 - - 4). We documented O. maculata records from 32 counties in peninsular Florida (Table 4).

We personally recorded O. maculata at 62 sites in Florida, including the earliest records in two counties: DeSoto (Arcadia; 18-Nov-2020; 27.2226, -81.8574) and Glades (Brighton Reservation; 18-Nov-2020; 27.0776, -81.0703). Our observations confirm those of other researchers that O. maculata most often grows in shaded areas with thick leaf litter. We most commonly found O. maculata growing in deeply shaded areas under slash pine trees (Pinus elliottii Engelm.) and oaks (Quercus spp.) at sites where fire has been suppressed and there is a thick layer of leaf litter on top of the sandy substratum. These were very often heavily disturbed sites by the side of roads and next to parking lots though O. maculata has also penetrated some local reserves. Oeceoclades maculata was one of the few plants growing on leaf-litter mats under Australian pine (Casuarina equisetifolia L.). Although ^{Stern (1988}) reported that O. maculata roots do not penetrate the soil beneath the leaf litter, we found many specimens' roots extending deep into the soil. Additionally, while many of our collections were found growing in leaf litter, we also found specimens growing in sandy soil and muddy areas, indicating an even wider range of suitable habitats. Many O. maculata records came from photographs posted online, most notably on iNaturalist, demonstrating the value of these outlets for community science. Photos are particularly useful sources of site records in areas where specimen collection is severely restricted (e.g., in Everglades National Park).

Discussion

Originally from Africa, Oeceoclades maculata has attained a broad distribution in the New World, ranging from the Atlantic rainforest of northeastern Rio Grande do Sul, Brazil (~28.5°S; ^{Colla 2014}), and Estancia Santa Teresa, Corrientes, Argentina (28.0°S; 1976; AL Cabrera; FMNH) in the south, to St. Augustine, Florida (29.9°N; 2022; Table 4) in the north (Fig. 2). Due to its original discovery in Brazil, ^{Hammer (2001}) suggested that O. maculata may be native to both Africa and South America. However, most researchers, including ^{Stern (1988}) and ^{Cohen and Ackerman (2009}), list it as originating in Africa. Considering the expansion of O. maculata's range as documented in this paper, it seems unlikely that it is native to South America. Oeceoclades maculata's spread to Florida is likely merely an extension of its invasion of suitable habitats throughout the New World.

All early records of O. maculata in the New World (1790-1900) are from South America, south of 2.5°S: in Brazil, Paraguay, Bolivia, and northern Argentina (red in Fig. 2A). By 1960, O. maculata had spread into northern South America as well (orange in Fig. 2A). Beginning in 1962, populations of O. maculata were found in other parts of the New World beyond South America (Tables 2-4). By 1990, O. maculata established scattered populations in Central America and Mexico, on several West Indian islands, and into Florida (green in Fig. 2). Since 1990, O. maculata has spread broadly through much of Central America, southern Mexico, the West Indies, and peninsular Florida (blue in Fig. 2). ^{Hammer (2001: 77)} states that O. maculata's appearance in Florida ''may be the result of a natural migration northward from tropical America as a result of global warming''.

Maps were generated using Carto (2021)

Figure 2 A. Records of Oeceoclades maculata in the New World. B. Records of Oeceoclades maculata in Florida. Red = 1790-1900, Orange = 1901-1960, Green = 1961-1990, Blue = 1991-2021. Older records overlay and may obscure newer records. 

Although O. maculata produces tiny, wind-dispersed seeds, it almost certainly first arrived in South America from tropical Africa by ship, probably unintentionally accompanying cargo or in dumped ballast. The ability of O. maculata to self-fertilize and its potential for vegetative propagation allows this species to establish new populations from a single individual. Though O. maculata possesses nectar guides and a nectar spur, there are almost no reports of outcrossing over its naturalized range, except for observations made by ^{Aguiar et al. (2012}) who observed two species of butterfly (Heliconius ethilla narcaea and H. erato phyllis) acting as pollinators in a population in Brazil. Nevertheless, ^{Ueno et al. (2015}) confirmed that most populations across their study site had low genetic diversity, with high genetic structure between populations, apparently as the result of predominantly self-pollination and vegetative propagation within populations established by a small number of individuals. Despite the absence of a reliable pollinator throughout the New World, these plants display high fruit set due to rain-assisted pollination (^{González-Díaz & Ackerman 1988}). The stamens and the stigma are fused into a column which is covered by a cap; when disturbed, the cap falls off and the pollinarium moves and contacts the stigmatic surface allowing for spontaneous self-pollination. In absence of rain as a disturbance, fruit set is dramatically reduced. Under optimal conditions, O. maculata can grow from seed to flowering in a single year (^{Adamowski 1999}).

After its arrival in the New World, O. maculata appears to have spread gradually both by wind and human transport. It took >170 years before the New World O. maculata populations were recorded beyond South America, and >20 years for the first Florida populations to expand beyond Miami-Dade County, indicating that O. maculata naturally disperses only relatively short distances per generation. Thus, it appears that wind may carry O. maculata seeds perhaps 10-20 km, not hundreds or thousands of kilometers. Long-distance colonization events, such as the arrival of the first populations of O. maculata in Guatemala, Mexico, Florida, and many West Indian islands, were most likely human-assisted.

Recently, ^{Kolanowska (2014}) modeled the ecological niche of O. maculata using climatic data from 15 Old World and 59 New World site records to estimate the worldwide distribution of the suitable habitats for the spread of this species. ^{Kolanowska's (2014}) analysis, however, used only a single Florida site, from MiamiDade County, for calibrating the model, which subsequently indicated that Florida should have habitat with suitable climate for this species only at its southernmost tip. Nevertheless, O. maculata populations have spread and are thriving across much of peninsular Florida. The question remains as to how far north they will spread. In the Köppen-Geiger climate classification system, the southeastern US has a humid subtropical (CFa) climate similar to that of southeastern Brazil, eastern Paraguay, and northeastern Argentina, areas where O. maculata records are common (see ^{Peel et al. 2007}).

^{Stern (1988: 968}) wrote: ''An example of the invasive capabilities, ability to colonize new ground and capacity to withstand extremes of temperature is the fact that plants of Oeceoclades maculata have persisted over the past four years in Gainesville, Florida. I observed several clusters of Oeceoclades maculata plants growing in leaf litter in dense shade under oaks and pines near my house. No doubt, these escaped from greenhouse cultivation as seeds and became established spontaneously.''

^{Hammer (2001}) reported the O. maculata populations in Gainesville dying out after a hard freeze (several hours below -2°C), suggesting that populations may not be able to persist this far north. The University of Florida Herbarium, however, has O. maculata specimens from Gainesville collected in 2001 and 2002 in neighboring sites, with the 2002 record (leg. J. Barichivich) annotated with: ''Locally abundant; persisting for three years as escapes from potted mother plant on front porch (mother plant transplanted from Miami lawn). Flowering and fruiting.'' In January 2020, Shannon Bieniek (pers. comm.) searched the Gainesville areas where O. maculata populations had been reported but did not find any. In April and May 2021, we also searched these areas, but did not find any O. maculata. We did, however, locate several individuals in Paynes Prairie Preserve, just south of Gainesville. In 2022, photos of O. maculata were posted on iNaturalist from three additional sites in the Gainesville area, and one site in St. Augustine in St. Johns County, the highest latitude population (29.9°N) known for this species, ~1.4° higher than the southernmost known records in South America (~28.5°S). This difference may relate to the tempering influence of the Gulf Stream on the climate of northeast Florida.

While O. maculata may reach its northern outdoor limit in peninsular Florida, limited by hard freezes, it seems likely that this species will continue to spread northward through eastern Mexico and eventually invade southeastern Texas, a region with a similar humid subtropical (CFa) climate to that of central Florida.

Although we found O. maculata primarily in heavily disturbed sites, many records come from relatively natural habitats. In Puerto Rico, ^{Cohen and Ackerman (2009}) found established populations of O. maculata in every class of forest they examined, from extensively disturbed areas to intact old growth forest. In fact, the second least disturbed forests, with 50-80% of tree cover remaining, hosted the largest O. maculata populations. ^{Cohen and Ackerman (2009)} found a significant negative correlation between the prevalence of O. maculata and the abundance of two native orchid species, although this could be due to differences in habitat preferences rather than any direct impact between the species. Similarly in Veracruz, Mexico, ^{Hágsater et al. (2005}) found a negative correlation between the density of O. maculata and native orchid density. ^{Cohen and Ackerman (2009)} suggest that this could be due to negative interactions between the species' mycorrhizae.

There are efforts to eradicate O. maculata in some natural areas, e.g., in Mexico, where it is classified as one of 23 high priority invasive plants (Aguilar et al. 2007). In 1991, as O. maculata was spreading in Miami-Dade County, the Florida Exotic Pest Plant Council (FEPPC) placed O. maculata on its list of invasive exotic plants that are impacting or have the potential of impacting native plant communities through displacement of native species, changing community structures or ecological functions, or hybridizing with native species (FEPPC 1991). In 2003, however, the FEPPC (2003) removed O. maculata from this list. Although O. maculata is thriving in peninsular Florida, its impact on native plant species in the New World appears to be minor, especially when compared with the many other invasive plants that plague Florida. Currently, there is just one orchid species on the FEPPC (2019) list: the Chinese crown orchid (Eulophia graminea Lindl.), a species that is quickly spreading in Florida, Texas, and the West Indies (^{Pemberton 2013}, ^{Ackerman & González-Díaz 2021}).

Oeceoclades maculata and many other non-native plant species are still sold online and at nurseries. Orchids in particular have a cachet and people struggle to view them as potentially damaging. Despite having many invasive attributes, people continue to cultivate O. maculata throughout Florida. A pot of blooming O. maculata is displayed in front of a neighbor's house in Stuart, Florida. She received them as a gift from a coworker. ^{Valdez (2020}) posted a video on YouTube of a potted O. maculata flowering in San Antonio, Texas, giving instructions on how to care for this species. Among those commenting on the video was a person in Malaysia who had received O. maculata from a friend. It seems to be only a matter of time before O. maculata spreads to everywhere worldwide where it can survive outdoors, either dispersing on its own or with human help, perhaps through escaping from cultivation, as documented in Gainesville, Florida. Whether it will have any major impacts in the areas where it invades remains to be seen.