''Silphium perplexum'' J.R.Allison is a

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

species in the

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

endemic to the state of

Alabama (We dare defend our rights) , anthem = "Alabama (state song), Alabama" , image_map = Alabama in United States.svg , seat = Montgomery, Alabama, Montgomery , LargestCity = Huntsville, Alabama, Huntsville , LargestCounty = Baldwin County, Al ...

. ''S. perplexum'' is commonly known as Old Cahaba rosinweed, a reference to the

Cahaba River The Cahaba River is the longest substantially free-flowing river in Alabama and is among the most scenic and biologically diverse rivers in the United States. It is a major tributary of the Alabama River and part of the larger Mobile River basin. ...

near which all populations of this species are found.

Etymology

The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

'perplexum' means perplexing.

Taxonomy

Old Cahaba rosinweed was described in 2001 by the botanist James Robert Allison. The species is thought to have arisen from a hybridization event between ''

Silphium integrifolium ''Silphium integrifolium'' is a species of flowering plant in the family Asteraceae. Its common names include rosinweed, whole-leaf rosinweed, entire-leaf rosinweed, prairie rosinweed, Despite ''S. perplexum'' having arisen from a hybridization event, it is not appropriate to treat it as a mere

hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...

as its distribution does not overlap with either of its parent species. From this it can be concluded that the species is self-sustaining. This means that its existence and future evolution are independent of the fate of its parent species. Furthermore, if Old Cahaba rosinweed were to be characterized as a

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

or even a

variety Variety may refer to: Arts and entertainment Entertainment formats * Variety (radio) * Variety show, in theater and television Films * ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont * ''Variety'' (1935 film), ...

, this would necessitate choosing if it had more similarities with ''S. glutinosum'' or ''S. integrifolium''. At present there is not a clear basis for selecting one over the other. To conclude, because populations of ''S. perplexum'' vary little in their morphology, are easy to distinguish from the parent species and occupy non-overlapping areas, there is a strong consensus that S. perplexum is a legitimate species. The ‘lifespan’ of this species (e.g., how long it has existed with few new additions from interspecific hybridization events) has been estimated by studying its distribution compared with its putative parents. Evidence suggests the species could not have formed post 1885 but no lower bounds on its origin have been proposed, therefore its age is uncertain. Tracing the ancestry of ''S. perplexum'' is complicated due to it being of hybrid origin. However, the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

of the ''

Silphium Silphium (also known as ''silphion'', ''laserwort'', or ''laser'') is an unidentified plant that was used in classical antiquity as a seasoning, perfume, aphrodisiac, and medicine. It also was used as a contraceptive by ancient Greeks and Romans ...

'' genus, including of one of its parent species '''S. integrifolium (the prairie rosinweed) is understood. ''S. integrifolium'' shares a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

with '' S. wasiotense'' and ''S. perfoliatum'' whilst being more distantly related to '' S. mohrii''.

Morphology

''Silphium perplexum'' is a

herbaceous perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widel ...

growing to a height of , it has short

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

s. Leaf morphology changes as the plant develops with

basal rosette In botany, a rosette is a circular arrangement of leaves or of structures resembling leaves. In flowering plants, rosettes usually sit near the soil. Their structure is an example of a modified stem in which the internode gaps between the lea ...

leaves differing from stem leaves. Stem leaves are around 30 cm long and are arranged alternately up the stem. Stem leaves are variable being either

ovate Ovate may refer to: *Ovate (egg-shaped) leaves, tepals, or other botanical parts *Ovate, a type of prehistoric stone hand axe *Ovates, one of three ranks of membership in the Welsh Gorsedd *Vates In modern English, the nouns vates () and ovat ...

lanceolate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

, they may attach to the stem directly with auriculate leaf bases. Alternatively, leaves may have short petioles with winged margins resembling leaflets. The leaf margins are usually smooth but may be

dentate Dentate may refer to: * A species having dentition * An energy-dissipating baffle block in a spillway * An individual not being edentulous * Dentate gyrus of the hippocampus * Dentate nucleus of the cerebellum * Denticity in chemistry * Dentat ...

. Almost the entire above ground surface of the plant is covered in glandular and pubescent

trichome Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...

s. Glandular trichomes are branched and amber colored, the glands secretions give the plant a resinous texture. Old Cahaba rosinweed has 'stipulate glandular trichomes' which are infrequently found in ''Silphium'' except for species such as ''S. laciniatum'' and the parent species of ''S. perplexum'', ''S. glutinosum''. This plant develops a basal rosette during its juvenile phase, however, basal leaves are usually lost by the time of flowering. At maturity, stems from one to eight feet are produced which do not branch below the inflorescences. ''Silphium perplexum'' flowers from July to October, their flowers are produced in much branched open

panicle A panicle is a much-branched inflorescence. (softcover ). Some authors distinguish it from a compound spike inflorescence, by requiring that the flowers (and fruit) be pedicellate (having a single stem per flower). The branches of a panicle are of ...

s with each stem holding as many as thirty. The flowers are

composite Composite or compositing may refer to: Materials * Composite material, a material that is made from several different substances ** Metal matrix composite, composed of metal and other parts ** Cermet, a composite of ceramic and metallic materials ...

, containing a cluster of fertile disk-florets surrounded by many bright yellow ray-florets averaging around 20 per

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...

. After pollination, simple dry-fruit are produced, the fruit are characterized as a cypsela along with the fruit of all other Asteraceae. Despite this, they are often incorrectly described as

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...

s. Old Cahaha rosinweed is often confused with its commoner parent species ''S. glutinosum''. This is due to similarities in their morphology, such as the presence of glandular trichomes on the involucral bracts, leaves and stems. In spite of the similarities, ''S. perplexum'' differs from ''S. glutinosum'' in several ways. Firstly, ''S. perplexum'' has taller stems with more numerous

nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

, its leaves are also more lanceolate with shorter petioles and larger blades. Also, flower heads are more elongated and the bracts surrounding the flowers have a more chartaceous (papery) texture. Each flower of ''S. perplexum'' contains a greater number of ray-florets than in ''S. glutinosum'' and they are of a deeper yellow.

Growth and reproduction

''Silphium perplexum'' can reproduce vegetatively through rhizome growth though the rhizomes are short, so spread slowly. Alternatively, this species can produce large numbers of seeds which are released when the seed heads shatter in autumn. ''S. perplexum'' commonly cross-pollinates with other ''Silphium'' species in natural environments so is liable to produce hybrid offspring. Hybrids observed include ''S. anteriscus'' x ''S. perplexum''.

Distribution and habitat

This species is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to only three counties in west-central Alabama, it has an extremely limited distribution with all populations less than 9 miles from the Cahaba River. Old Cahaba rosinweeds favor soils overlying chalk, this contrasts with the parent species ''S. glutinosum'' which prefers growing over dolomite or limestone. ''S. perplexum'' is most numerous in prairies and openings within scrub and forest. This species is found alongside other tallgrass-prairie plants including grasses such as ''

Andropogon ''Andropogon'' ( common names: beard grass, bluestem grass, broomsedge) is a widespread genus of plants in the grass family, native to much of Asia, Africa, and the Americas, as well as southern Europe and various oceanic islands. Over 100 spec ...

'' L. spp. and ''Schizachyrium'' ''scoparium'' (Michx.) Nash. as well as legumes including ''

Desmanthus illinoensis ''Desmanthus illinoensis'', commonly known as Illinois bundleflower, prairie-mimosa or prickleweed, is a common plant in many areas of the south central and Midwestern US. Habitat It can often be found growing on the sides of roads, needing fu ...

'' (Michx.) MacMill. ex B.L.Rob. & Fernald. and shrubs including '' Rosa bracteata'' J.C.Wendl.

Conservation

Due to this species very restricted range and low population numbers within Alabama it has been listed as an S1 species by ‘ Nature serve’. This means that ''Silphium perplexum'' is at a high probability of extinction unless conservation action is taken. Despite the recognized threats to this species, ''S. perplexum'' is not listed on the U.S
Endangered Species act
or th
IUCN red list
The lack of conservation attention could be due to uncertainty surrounding ''S. perplexum's'' species status.

References

{{Taxonbar, from=Q15564227 Flora of Alabama perplexum Plants described in 2001