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
Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...
endemic to the state of
Alabama
Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...
. ''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. It is a major tributary of the Alabama River and part of the larger Mobile River basin. With headwaters near Birmingham, the Cahaba flows southwest, then at Heiberger tu ...
near which all populations of this species are found.
Etymology
The
specific epithet
In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...
'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 diff ...
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 Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
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 or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...
of the ''
Silphium
Silphium (also known as ''laserwort'' or ''laser''; Ancient Greek: , ) is an unidentified plant that was used in classical antiquity as a seasoning, perfume, aphrodisiac, and medicine.
It was an essential item of trade from the ancient North Af ...
'' genus, including of one of its parent species '''S. integrifolium (the prairie rosinweed) is understood. ''S. integrifolium'' shares a
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
with '' S. wasiotense'' and ''S. perfoliatum'' whilst being more distantly related to '' S. mohrii''.
Morphology
''Silphium perplexum'' is a
herbaceous perennial
In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...
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 Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
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, but they can also be at the top of an otherwise naked branch or trunk. Their structure is an ex ...
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 or ovate, a term for ancient Celtic bards ...
or
lanceolate
The following terms are used to describe leaf plant morphology, morphology in the description and taxonomy (biology), taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade ...
, they may attach to the stem directly with
auriculate
The following terms are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade is divided into two or more leaflets) ...
leaf bases. Alternatively, leaves may have short petioles with winged margins resembling leaflets. The leaf margins are usually smooth but may be dentate. 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 plant ...
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
In botany, 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 p ...
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 material ...
, containing a cluster of fertile disk-florets surrounded by many bright yellow ray-florets averaging around 20 per
inflorescence
In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...
. 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 fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...
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).
Node may refer to:
In mathematics
*Vertex (graph theory), a vertex in a mathematical graph
*Vertex (geometry), a point where two or more curves, lines, ...
, 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 only 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 foun ...
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 speci ...
Desmanthus illinoensis
''Desmanthus'' is a genus of flowering plants in the mimosoid clade of the subfamily Caesalpinioideae of the pea family, Fabaceae. The name is derived from the Greek words δεσμός (''desmos''), meaning "bundle", and ἄνθος (''anthos'') ...
'' (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
NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and the public. Na ...
’. 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.