The Cover Story
“The Melastomataceae are among the 10 largest families of flowering plants with an estimated 173 genera and some 5858 species.” Ulloa, et al, in Goldenberg, et al, 2022.
The Melastomes are a nifty group, given their characteristic floral structure and, especially in larger-leaved plants that so frequently show incredible venation (the complete secondary veins running from base to tip make this an “acrodromous” pattern). Within this family, our Rhexia (the only Melastome native to the Panhandle) is an outlier, ecologically, geographically, and systematically. While the great bulk of species in the family are tropical, Rhexias are among the few temperate representatives. Yes, you’ll see Tibouchina for sale in local nurseries, and certainly encounter some of the exotic representatives in South Florida, or on trips to the tropics. There are many showstoppers in this handsome assemblage, our Rhexias being no exception.
How do you know the plant in question is a Melastome, much less a Rhexia? In the Apalachicola flora, a very few characters will almost certainly get you to the right genus If you find an herb with opposite leaves, and flowers with 4 petals atop a jug-like “inferior” fruit (a swollen base and cylindrical neck) topped by a rim made of 4 angular calyx lobes, you’ll be looking at a Rhexia. The 8 elaborate stamens are an added dividend. Practically the only chance of confusion would arise with the few Ludwigias (Onagraceae) that have opposite leaves. Those will all have yellow flowers with capitate (knob-shaped) styles.
The Main Story
The ISB Atlas lists ten Rhexia species we expect to encounter in the Apalachicola flora. To me, they break into 4 groups (most of which fall into what I call the Mariana-Virginica complex):
- the Alifanus type – tall & virgate (wand-like), glabrous (lacking haris) and glaucous (washed with a whitish bloom), largest blossoms of our Rhexias, flowering peak in May, but lasting into fall – one species, Rhexia alifanus.
- the Petiolata type – contrite and leafy, small flowers with unspectacular stamens – two species, Rhexia petiolata & Rhexia nuttallii.
- the Lutea type – herbaceous, yellow flowered with hairy leaves, small anthers in deep yellow flowers, produced early (April – June) – one species, Rhexia lutea
- the Mariana-Virginica types – common, white to lavender-pink flowers, spring through summer – five species, along with their hybrid-swarm-like variants. It’s tempting to separate the Virginica type, which is the exuberant, winged-stem “Handsome Harry”, but grouping broadly, we find Rhexia mariana, R. virginica, R. nashii, R. parviflora, R. cubensis, and R. salicifolia. I have yet to encounter plants representing the last three species.
It’s worth introducing contemporary background, with a quotation from Judd, et al (2022).
“The genus is systematically difficult due to extensive polyploidy and hyridization, resulting in hybrid speciation and a highly reticulate phylogeny. Molecular data strongly support the allopolyploid origin of R. nashii, with diploid R. mariana and R. virginica as the genomic source species (i.e. Rhexia nashii has it origins in hybrids between R. mariana and R. virginica).,,, Although not as well investigated, molecular and/or morphological evidence of hybrid speciation has been suggested for R. cubensis, R. salicifolia, R. lutea, R. interior, and R. ventricosa by Ionta et al…; most of these species are polylploids, except for R. salicifolia and some individuals or R. cubensis… As a result of polyploidy and hybridiaztion, phylogenetic relationships within Rhexia are still rather unclear.”
Rhexia lutea – the Yellow Meadowbeauty
Best to parse out the most easily identified first. Rhexia lutea is unmistakable, as the only species with yellow flowers. This is a cinch, as long as the plant’s in flower. The challenge comes later in summer, when the deep golden yellow blossoms have faded, but it isn’t impossible.
The plant remains recognizable. Most usefully, the fruiting structure is practically spherical, with a conspicuously constricted neck.
The larger (main stem) leaves, are about as long as my finger is thick. Note the spiny margins and the subtle, yet distinguishable pair of marginal veins.
About the only plants, at a distance, that might get confused with Rhexia lutea are some of the Ludwigias, lovely 4-petaled yellow flowers bobbing in the morning on their wand-like stems or more couched in foliage of branching herbs. And there are many 4-merous Ludwigias around. Below you’ll see two photos of Ludwigia virgata.
Rhexia alifanus – Savannah Meadowbeauty
Though Rhexia lutea is the most quickly segregated, Rhexia alifanus is the true outlier, not simply as compared to other plants in our flora, but within the genus, and across the range (currently 13 species, native from the eastern half of North America into the Antilles).
Vegetatively, R. alifanus stands up as distinctive, being the most wand-like (virgate), typically unbranched (ramifying in the inflorescence), and bearing regularly spaced pairs of opposite (occasionally whorled with 3 leaves), lanceolate, entire, glaucous, upturned to clasping leaves. Stems are normally 0.4-0.6 m, but can be shorter, as well as taller, reaching 1 meter.
This strategy makes Rhexia alifanus particularly suited to areas cleared by fire or other irregular removal of understory. With age, the woody underground base can become quite large, and possibly persistent. Entire open areas, such as wet prairies and light-canopied pine flatwoods (cleared by regular fires), can be populated with thousands of plants.
Rhexia petiolata (& Rhexia nuttallii) – Fringed Meadowbeauty
Not uncommon, yet often unseen, Rhexia petiolata (and it’s hairless twin, R. nuttallii, which I’ve not seen) are readily distinguished from others in the genus. If you have flowering material, these are the plants with tiny stamens, radically distinct from their pink cousins. But even without good flowers, the plants set them apart. Yes, they have petioles, but they have petioles only from the viewpoint of other white and pink-flowered Rhexias, in which leaves broadly join the stems. They are, curiously, more similar to Rhexia lutea in having small stamens and short leaf stalks that can be called petioles.
Pairing with Rhexia petiolata, taxonomists include the smaller Rhexia nuttallii, a plant distinguished by: 1) its small size (just a few inches tall, as compared to R. petiolata, which reaches well over a foot in height as the season progresses) and 2) its ovary, which bears stipitate glands.
However, the single population I’ve studied (discovered by David Roddenberry) is mixed, with plants showing both conditions. In the photo below, I’ve paired ovaries from two plants that were collected within feet of one another, and are vegetatively indistinguishable. Next flowering season, we’ll give these concepts more attention.
Rhexia mariana and Rhexia nashii
The plants that most have confused me (and continue to do so) are Rhexia mariana and Rhexia nashii. When I encounter the most common Meadowbeauty, the delicate plant with almost linear leaves, the shorter plant (usually under 30 cm) that’s ever-present along roads and paths, the one that often occurs in colonies of mostly creamy white or shades of light lavender pink, the one in which petals seem always to turn under along the edges, then I think I looking at the plant that is Rhexia mariana (see below).
When I encounter a plant that can be in the same size range, but will continue to shrub-up, one with broader foliage, sometimes narrowly ovate-acuminate, and other times narrower, but always distinguished by larger flowers that show as a clear deep lavender pink (and the petals present as more planar), then I inspect buds and open flowers to see if the petal reverse sides bear stipitate glands, and check to determine whether the hypanthium is at least 1 cm long. If so, these are the plants I call Rhexia nashii. But there is much foliar variation of plants that key to R. nashii.
Rhexia virginica – Handsome Harry
I manage to understand Rhexia virginica by insisting it’s the plant with conspicuously-winged stems. That seems to accompany a robust and growingly-shrubby habit. I first see flowering specimens after Rhexia alifanus has past its peak flowering (May into early June). The flowers are a rich lavender-pink, born in multi-branched inflorescences.
Hybrids….
As Yul Brenner sang, 4,625 times on stage: “But is a puzzlement”. In early June, I encountered a mixed population in the Box R WMA (Apalachicola). It was a party, and and almost everyone came. Of course, Rhexia alifanus and R. lutea were present, and behaved themselves. But the rowdy crowd was exhuberant. Plants perfectly expressive of Rhexia mariana, R. nashii, and R. virginica were in flower, as were all sorts of intermediate forms. It seemed I was in a hybrid swarm. Small colonies (recall, these plants can be rhizomatous) of various clearly recombined forms were all abundant. In a way, this was satisfying, forcing me to reflect on the range of variation I encounter in other locations, and causing me to accept the lack of absolute definition. I made a quick video, quick because the plants wilt and lose petals in bright sun and with the least disturbance. But I post it below, so you can experience a bit of what I saw:
The Back Story (It’s extensive)
“About 64% (3741) of the species of the Melastomataceae occur in the Americas, 25% (1472) in Asia and Oceania, 5.5% (349) in Madagascar, and 5.5% in continental Africa (326). The family is subcosmopolitan, mainly distributed in tropical and subtropical regions, but some species reach temperate latitudes. Melastomes range in elevation from sea level to about 4500 m in the tropical Andes of South America. Although some species occur in seasonally dry habitats in Africa, Madagascar, Sri Lanka, Thailand, and Brazil, there are no Melastomataceae in true desert environments. No genera are native to both the New and Old Worlds, but a few genera are disjunctly distributed between Africa, Madagascar, and Asia, e.g., Lijndenia, Medinilla, and Memecylon.” Ulloa et al, in Goldenberg et al, Systematics, Evolution, and Ecology of the Melastomataceae, 2022
Though the Melastomes are predominantly New World, the type for the family is Melastoma malabathricum L., one of the “25%”, i.e. 1472 species, native to Asia and Oceania. The story of this family and its naming developed through two overlapping cultural life stories, that of Linnaeus and his cronies, and the saga of the de Jussieu clan.
Linnaeus included Melastoma and Rhexia in the 1st edition of Species Plantarum (1753), but his organization, his “System” for grouping plants was based on the very modern understanding (in the 18th century) that anthers and pistils are sexual organs, and the incredibly functional classifying of plant genera based on the numbers and disposition of those same anthers and pistils. Linnaeus’s explanations were well-documented in editions of books on his Philosophy, his System, the Genera, and the Species.
Linnaeus’s System led to odd disjunctions, some involving our native Meadowbeauties. He filed (classified) Rhexia as well as Osbeckia, another Melastome, as OCTANDRIA, MONOGYNIA, which was his Class (Octandra) of plants with 8 stamens, and within that, his Order (Monogynia) of plants with a single pistil. Melastoma, however, showed ten stamens, thus Linnaeus pigeonholed that genus in his Class DECANDRIA; within that Class, it fell out as MONOGYNIA, plants with a single pistil. He was an orderly person, an accountant, the “bean counter” of botany.
The botanists in Paris, however, were looking at plants differently. Plant and animal species were links in the great Chain of Life, and genera were segments of that Chain. The segments belonged together, and the Chain was unbroken, even as more species were described and the concatenating segments were found (inconveniently) to branch and cross over from place to place. Patterning the organization of genera into groupings should reflect the basic arrangement to be discovered in the Chain of Life. Keeping like with like was thought more “Natural”, as opposed to Linnaeus’s hard and fast accounting, which came to be regarded as “Artificial”. The natural approach was accomplished by looking at all of ( or at least what seemed to be the most important) the parts and pieces, not by the simple method of counting numbers of stamens and pistils. The de Jussieu family was all in.
A good place to step into this story is 1754, the year following publication of Species Plantarum, when the brilliant Michel Adanson returned to Paris after 5 years exploring Senegal under sponsorship of the French East India Company. Adanson had different ideas for the materials he had collected – he imagined a grouping based on the greatest accounting of similarities, beginning his proof with seashells. By 1763, however, Adanson had published Familles naturelles des plantes. Cultures were clashing, at least the colors were showing. This was still within the heyday of Linnaeus. Adanson’s ideas weren’t immediately celebrated, but he persisted. In 1774, he exhausted a Committee of the French Academy of Sciences with a major submission – described in Wikipedia as:
“an immense work, extending to all known beings and substances. It consisted of 27 large volumes of manuscript, employed in displaying the general relations of all these matters, and their distribution; 150 volumes more, occupied with the alphabetical arrangement of 40,000 species; a vocabulary, containing 200,000 words, with their explanations; and a number of detached memoirs, 40,000 figures and 30,000 specimens of the three kingdoms of nature.”
Of course, Adanson wasn’t alone. He was in the circle of botanists centered on the Jardin du Roi (today, the Jardin des plantes), where Antoine Laurent de Jussieu would come to work (and stay to rule) from 1770 to 1826. A.L. de Jussieu was nephew to three botanical uncles, the rising star of a botanical dynasty. His associate Adanson had introduced the idea of natural plant families, and his uncle, Bernard de Jussieu had planted royal gardens in groupings reflecting natural order, but A.L. de Jussieu rose to the task of coalescing and publishing an overall Natural System. His Genera Plantarum went to the printers in 1789, on the very eve of the French Revolution.
In the world of plant classification (Systematics), the conception of Melastomes as a natural family dates to 1789, when A.L. de Jussieu described Class XIV, Order VIII, bringing together 9 genera – “Blakea Brown (in) L., Melastoma Brum. (in) L., Tristemma (gen. nov.) Topobea Aubl., Tibouchina Aubl., Mayeta Aubl., Tococa Aubl., Osbeckia L., and Rhexia Gron. in L.” The legacies were far-reaching. Linnaeus established binomial nomenclature as the standard way to name plants, but de Jussieu, in 1789, founded the modern system of plant classification.
Rhexia was there, from the start. We need to go back in time to relate the story of Rhexia, beginning with John Clayton, an Anglican minister who moved to Virginia at age 20 (in 1725), eventually assuming the position as Gloucester County clerk, which he held for 53 years. In addition to his work, and management of Windsor, his 450 acre property, Clayton became one of North America’s earliest botanists, collecting plants and even writing descriptions, which (of course) he sent to England.
Clayton was early, but not the first to send plant specimens to England. Before him was John Banister (who was killed by a stray bullet in 1692 while on a field trip), and a series of people sent from England by the discordant and competitive group of naturalists called “The Botany Club” (Reveal, 1983). You might run into the names of people who were collecting plants for English naturalists – Hugh Jones, William Vernon, David Krieg, John Smart, Joseph Lord, and John Lawson (who was killed by Tuscarora Indians in 1711.) Their work stoked some interest, but on the heals of Banister’s celebrated and productive period, the magic was not there. Two decades would pass until arrival of the next person to make significant in-roads in the study of North American plants. Enter Mark Catesby, who joined his sister in moving from the family home in Essex to live in Willimsburg in 1712. Catesby explored the region for several years, returning to England in 1719 with a treasure chest of specimens, the significance of which helped generate financing for a second, more extensive journey to the New World, in 1722. On his second return to England, Catesby began work on the Natural History of Carolina, Florida and the Bahama Islands, issued in parts, between 1729, through the supplement in 1747.
It was to the accomplished and notable Catesby that John Clayton sent his collections and notes (said to include his plant descriptions) in 1734. Catesby was focused on his own material, laboring over collections with little financial support, drawing most of the illustrations, and learning to etch plates to save costs. He forwarded Clayton’s material to Jan Frederik Gronovius, a Dutch patron and collaborator of Linnaeus. It fell to Gronovius to study the specimens, among which was material of the plant we know today as Rhexia virginica. Gronovius issued his descriptions in two volumes (1739 and 1743) as Flora Virginica, but it’s clear the collector, Clayton, was neither informed nor involved with the Flora. Evidence suggests this struck Clayton as appropriation, for only in later publications did Gronovius and Linnaeus fess-up and recognize Clayton’s efforts.
That history brings us to the publication of Rhexia virginica and Rhexia mariana in the first edition of Species Plantarum (1753). Linnaeus made it evident his work was grounded in existing publications, including that of Gronovius, who had applied the name Rhexia to a plant in his publication, Flora virginica. As with other species in his Flora, Gronovius knew the plant from Clayton’s material. And Gronovius was up on the literature; he knew English botanists had examined and published information on similar specimens years before. Leonard Plukenet published an illustration of the plant eventually to be called Rhexia in the third volume of his astonishing Phytographia (1692), followed by textual notes in Almagestum Botanicum (1696), in which he labeled his specimen Lysimachia non papposa virginiana…..) Below is that plate from Phytographia (Figure 8, 1692, the on-line digital records of Madrid’s Jardín Botánico Real) in which he notes the first specimen was collected by Banister.
A few years later, in his 1705 Amaltheum Botanicum, Plukenet recorded another example, from the Carolinas, this time designating the plant as “Alifanus vegetabilis Carolinianus – The Sucking Bottle.”
But Plukenet’s “Alifanus” would be kept in synonymy, resurfacing in 1788 as the specific epithet for Rhexia alifanus. In recent years, the origin of Plukenet’s term has seemed obscure, but that was not always true. Charles James, in his 1956 monograph of the family, explains:
Reasonable? Absolutely. Noting Plukenet’s use of the “Sucking Bottle” and following up on James’s lead, we learn of an Italian town, Allifana (Now Alife), that was known for the production of large drinking cups called “allifani.” Arcane, but logical.
Alifanus was an option as the name for our genus. Citing both of Plukenet’s entries, Gronovius could have elected to name his plant “Alifanus”, but applied the name Rhexia. Here too, it remains something of a mystery as to why he chose that name, which suggests it can be used to staunch wounds. Thomas Meehan, in his lovely 1879 book, The native flowers and ferns of the United States in the botanical, horticultural and popular aspects, gave this conundrum some attention,
“Linnaeus, in his Philosopia Botanica, under the head of names derived from medical virtues says it is from the Greek rhexis, which signifies a rupture….The authority for these statements is, however, not very apparent; and it is a singular fact that not only the genus, but the whole order to which it belongs, seems to be strikingly destitute of medical qualities…”
accompanying his discussion with an illustration (from Biodiversity Heritage Library):
With the Banister-Plukenet-Clayton-Gronovius history, we arrive at the entry gates to modern taxonomy, the publication of Species Plantarum. Linnaeus was aware of the literature. Citing his sources. he folded Gronovius’s work into his text, accepting the genus Gronovius published. In the figure below, you can see his actual entry for Rhexia (image borrowed from Biodiversity Heritage Library, provided through Missouri Botanical Garden).
For over two centuries, authors basically have given Linnaeus credit for Rhexia and approximately 1,000 other genera and 6,000 species he treated in Species Plantarum. Recent practice moves to restore credit to authors who published works on which Linnaeus relied for his 1753 botanical landmark. In ISB, Rhexia remains credited to Linnaeus – Rhexia L., but the standard among Melastomologists (and in the on-line Flora of North America) has become “Gronovius in Linnaeus”, the “in” telling us the writer accepts Gronovius as the author of a genus published in Linnaeus’s book. This is actually the way A.L. de Jussieu cited the genus. Yet more absolute is the current entry for Kew Index on-line, which cites “Rhexia Gronovius”. So authorship is clear. I guess you could call this woke, but it’s a valid point. Gronovius, however, used polynomials (names with several modifying terms) for his species (even in the 1762 edition), thus Linnaeus retains credit for the specific name of the type, which is written Rhexia virginica L.
In older publications, you’ll see Linnaeus credited with the genus Rhexia, but had it not been for the working relationship with Gronovius (as colleague and sponsor), Linnaeus might have selected the earlier Plukenet name, Alifanus. Then we might have called these plants the “Sucking Bottles.”
The Side Story
The Melastomataceae teaches us several lessons. One, right off the bat, is that plant family names are generated and codified by absolute formula. From the International Code:
18.1. The name of a family is a plural adjective used as a noun; it is formed from the genitive singular of a legitimate name of an included genus by replacing the genitive singular inflection (Latin -ae, -i, -us, -is; transliterated Greek -ou, -os, -es, -as, or -ous, including the latter’s equivalent -eos) with the termination -aceae (but see Art.18.5). For generic names of non-classical origin, when analogy with classical names is insufficient to determine the genitive singular, -aceae is added to the full word. For generic names with alternative genitives the one implicitly used by the original author must be maintained.
Consulting William T. Stearn’s bible of form, Botanical Latin, we learn the word for “stoma” (which means “mouth”) demands an odd type-III declension, in that the root is “stomat-“, making the genitive singular “stomatis.” The family suffix (-aceae) doesn’t complete the generic name Melastoma, rather it takes the compliant form, “Melastomatis…” sacrifices the inflection “is“, yielding Melasomataceae, rather than the Melastomaceae. There must have been some discussion historically. In 1846, John Lindley, who formalized the endings we use for plant groupings, called these plants Melastomaceae in his publication, The Vegetable Kingdom...
So many thanks to Dr. Frank Almeda (Cal Academy of Sciences) for providing access to the recent publication Systematics, Evolution, and Ecology of Melastomataceae, 2022, Goldenberg, Michelangeli, & Almeda, editors.
As well as appreciation to Jerry Pitts, Box R Manager, and Toni Brannon, Regional Permits, for assistance in obtaining permits and access to the Box R WMA, Apalachicola, FL
Video Supplements
Below, you should see a video, which walks you through a keying excercise, getting to Rhexia mariana
Page Last Updated – 22 August 2023