Trichomanes holopterum Kunze has been known from the Big Cypress National Preserve (BICY; FL) since at least 1964, when it was first collected by R. and R. Stone (Delchamps, American Fern Journal 56:138–139. 1966). Abundant locally, it grows epiphytically on the bases, knees, and occasionally stumps of cypress (Taxodium spp. Rich), on semi-decomposed parts where mosses and liverworts are also abundant. Stands where T. holopterum have been found also tend to possess a sub-canopy dominated by cocoplum (Chrysobalanus icaco L.) beneath the deciduous cypress canopy, the former likely contributing to maintenance of high-humidity conditions important to members of the Hymenophyllaceae, particularly during the winter when the cypress drop their leaves.

In January 2024, a team of volunteers including Andrew Skok and Virginia Palmer-Skok, accompanied by BICY staff were surveying one of the known sites of T. holopterum. There, Mr. Skok photographed an individual sporophyte that appeared much larger than typical T. holopterum. These photos were shared with the lead author, who then began to investigate descriptions of other Trichomanes that better suited these individuals, consulting first the Flora of the Republica de Cuba (Sánchez, Koeltz Scientific Books. 2000) and the Ferns of Jamaica (Proctor, British Museum (Natural History). 1985). It quickly became clear that this was very likely a different species, but that closer examination would be required.

On March 8, 2024 the lead author visited the area with colleagues and collected specimens of both entities. The larger entity was later identified as T. galeottii E.Fourn, a highly variable species known from Cuba and Central and South America (Central Mexico to Ecuador). Trichomanes galeottii was first described by French botanist Eugéne Pierre Nicolas Fournier in 1868 based on collections made by Charles Wright, a protege of Asa Gray, though the description leaves much to be desired. He notes merely (translated from the original French) “There is a species of the West Indies and Mexico, variously and always misnamed until now, which differs from T. gardneri [Bosch] by its habit, and in particular by its narrower and more elongated [sporangial] receptacle, which we designate by the name of T. galeottii” (Fournier, M. E., Bulletin de la Société Botanique de France 15:143–148. 1868). The reader is then provided with a key wherein both T. galeottii and T. gardneri are separated from T. crispum L. by having lanceolate leaves, with those of T. crispum being ovate. Trichomanes gardneri is now considered a synonym of T. crispum, thus leaving the modern reader confused. Additionally, it should be noted that in the above quote, Fournier clearly used the word “réceptacle”, whereas in the key he distinguishes T. gardneri and T. galeottii by the latter having a longer, sub-cylindric “capsula”. “Capsula” clearly refers to the involucre, while the use of “réceptacle” refers to the sporangial receptacle, the eponymous “bristle” of members of the genus Trichomanes, which are commonly referred to as “bristle ferns”. It is unclear why he chose to refer to the sporangial receptacle in the text and the involucre in the key, since both appear elongate relative to T. crispum.

Morton, when dividing the clades of Hymenophyllaceae, placed both T. galeottii and T. holopterum in Trichomanes subgenus Achomanes section Achomanes subsection crispa, characterized by 1) leaves in fascicles that are 2) simply-pinnate with 3) simple trichomes, and with 4) veins that lack accessory wings that are not in the plane of the lamina (Contributions from the United States National Herbarium 38:153–214. 1968). He provided no further descriptions or distinctions between the two. Within subsection crispa a subgroup of species with lateral laminar wings over the majority of the petiole, which includes T. holopterum, was recognized as distinct from species included in the T. crispum complex, which includes T. galeottii, by Windisch (Bradea 6:78–117. 1992). Windisch's treatment of the T. crispum complex separates T. galeottii by its basal primary segments projecting either at right angles or upward on the rachis, trichomes on a more-or-less distinct basal cell, and the petiole alate, generally on the distal half. The narrowly alate upper petiole of T. galeottii makes it appear superficially intermediate between T. crispum and T. holopterum, which contain non-alate and prominently alate petioles, respectively. Windisch notes that “more biological data is needed for a better understanding of [T. galeottii and T. crispum], and also the relationship of [T. galeottii] with T. holopterum and closely allied species from sect. Achomanes”. Stolze suspected that T. galeottii was merely a variety of T. crispum (Fieldiana 39:1–130. 1976), but Windisch felt that intermediate individuals between the two were more likely of hybrid origin (1992). To be sure, the identity and relationships between many species of sect. Achomanes were tenuous at best for decades. However, a recent phylogenetic analysis by Dubuisson et al. (Botanical Journal of the Linnean Society 198:215–239. 2022) found that T. galeottii was in fact distinct, though indeed very closely related to T. crispum despite the latter lacking alate petioles. Dubuisson et al. describe the shared trait of their clade being long, simple hairs on laminar margins (2022). Trichomanes holopterum was represented in a distinct clade characterized by glabrous laminar margins, containing both winged and non-winged members.

In Florida, distinguishing individuals in the field proved difficult, as smaller sporophytes of T. galeottii superficially resembled T. holopterum in general size and habit, with both species possessing an alate petiole. Larger, mature sporophytes of T. galeottii were easily distinguished vegetatively by their overall size and longer petioles only narrowly winged, and that in the distal portion. However, in the field the petiole was regularly obscured by a dense cushion of bryophytes, making this character not altogether obvious on a passing inspection. It should also be noted that the largest leaves of T. galeottii were found growing terrestrially in humus, however, even epiphytic individuals grow larger than T. holopterum. Another vegetative character of note is the degree to which the rachis is winged. The thickness of the wings of the rachis in T. galeottii generally do not exceed the width of the rachis, while in T. holopterum the thickness of the wings is nearly twice that of the rachis (See Figs 1 and 2).

Fig. 1.

Trichomanes galeottii specimen from BICY, displaying the largest leaves observed in the center of the sheet, in addition to other, smaller mature specimens, and immature leaves in lower left. Note length of sporangial receptacles and wings of rachis and petiole (Lange 325).

Fig. 2.

Trichomanes holopterum specimen from BICY, displaying the largest leaves observed in the center of the sheet, in addition to smaller, mature leaves on the far left and far right, and immature leaves center right. Note length of sporangial receptacles and wings of rachis and petiole (Lange 326).

Large, mature specimens of T. galeottii are not likely to be confused with T. holopterum, but even smaller, or immature individuals can be readily separated by characteristics of the indumentum (Fig. 3). A character noted by Proctor (1985) is the presence of minute, clavate trichomes on T. holopterum, and in fact these were the predominant form on specimens examined in this study. He also notes the presence of minute, single-celled and scattered, acicular, multicellular trichomes, both of which were also present on T. holopterum specimens we examined. Trichomes on T. galeottii are best observed on the abaxial rachis and are generally long (by comparison) and single-celled atop a distinctly bulbous cell, these sometimes dark. Occasionally trichomes are multi-celled, but rarely clavate (Fig. 3). The Flora de la Republica de Cuba (2000) separates the two species based on T. holopterum's glabrous laminar margins, noting that T. galeottii can appear nearly glabrous but will always contain some marginal hairs. Florida material of T. galeottii certainly was sparsely adorned on the margins. We did, however, find occasional hairs on margins of T. holopterum, all of which were minute and clavate.

Fig. 3.

a.) in situ specimen of T. galeottii growing epiphytically at the base of Taxodium; b.) pin-nae of in situ T. galeottii displaying simple marginal trichomes, c.) abaxial rachis of T. galeottii disaplying predominantly simple trichomes atop darkened, bulbous basal cells (Lange 325); d.) abaxial rachis of T. holopterum displaying predominantly clavate trichomes along with multicellular, acicular trichomes (Lange 326); e.) narrow, elongate involucres of T. galeottii (note simple marginal trichome and larger cell size on lamina; Lange 325); f.) conic, widely flared involucres of T. holopterum (Lange 326). White scale bars = 1 mm. Photos a and c-f by J. Lange. Photo b by K. Bradley.

Fertile specimens of any size are most easily separated by the size and shape of the involucre, and the length of the sporangial receptacle. The involucre of T. galeottii, as described by Fournier, is narrow (1 mm) and elongate (2.8 mm), and weakly, if at all, flared at the apex. The involucre of T. holopterum is shorter (1.5 mm) and distinctly conic with a widely flared apex (1.3 mm). The sporangial receptacle is also much longer on T. galeottii, ranging between 3-15 mm, while those of T. holopterum we observed were between 2-4 mm (Fig. 3).

In discussing T. holopterum in Florida, past authors consistently noted that sporophytes are rare in the landscape, and where found remain small and rarely fertile (Delchamps, American Fern Journal 56:138–139. 1968; Farrar & Wagner, Botanical Gazette, 129:210–219. 1968; Farrar, University of Michigan. 1971; Nauman, American Fern Journal, 76:179–183. 1986). Comparisons were even drawn to Vittaria appalachiana Farrar & Mickel, a fern famous for its long-lived, gametophyte-dominant populations with sporophytes generally absent or abortive (Wherry, Science Press, Lancaster, Pennsylvania. 1942; Farrar, American Journal of Botany 65:1–12. 1978; see Farrar 1971). This description of Florida populations has been echoed in various sources, including the Flora of North America, as if static and permanent (Farrar, New York and Oxford. Vol. 2. Accessed 2024). However, in 2024, the authors observed sporophytes of T. holopterum to be rather common where found, with mature, fertile sporophytes being very much the norm. Without knowing the exact areas previous authors examined and at what level of detail, it is impossible to make parallel comparisons regarding proportions of generations observed. Despite this, it appears that sporophytes have become far more common over the decades and that they are in fact regularly fertile. This corresponds with increasing temperatures and a lack of winter freezes in recent years, which may be creating conditions more favorable for these tropical ferns at the northern extent of their geographic range, though this is largely speculative at this point.

Trichomanes galeottii is the third species of fern with an affinity for high-quality natural areas that has been added to the flora of South Florida in the last two decades, the others being Thelypteris sancta (L.) Ching (Bradley, American Fern Journal 96:112–114. 2006) and Goniopteris moranii C.Sánchez (syn. Thelypteris guadalupensis (Wikstr.) Proctor; Lange & Angelo, American Fern Journal 110:75–78. 2020). It may be too that like T. holopterum, T. galeottii has been present predominantly as gametophytes, and thus overlooked. Based on examination of an exquisite photo taken by fern explorer Alan Cressler, dated 2007, it is the authors' belief that T. galeottii has been present in Florida since at least that time, potentially earlier. Regardless, it is here confirmed through collections and field observations, that the congeners T. galeottii and T. holopterum are both extant and sympatric in BICY. The delicate nature of T. galeottii, along with its presence in such high-quality habitat and absence from the horticultural trade combine to make this highly unlikely to be associated with any anthropogenic means of introduction. We suggest that this be viewed as a natural range expansion and that T. galeottii be treated as native to the flora of Florida and the United States. Further range expansions of the Neotropical flora will likely continue in South Florida with climatic shifts and ongoing exploration within this floristically-transitional region.