Apium
Apium is a genus of flowering plants in the family Apiaceae (carrot or celery family), consisting of approximately 12 accepted species of annual, biennial, and perennial herbs. These plants are characterized by dissected leaves, small white to yellowish flowers arranged in umbels, and fruits that are schizocarps typical of the Apiaceae. The genus is primarily native to temperate and subtropical regions of the Old World, extending from Macaronesia and Eurasia to the western Himalaya, as well as southern South America including Bolivia, Brazil, and subantarctic islands.[1] The most prominent and economically significant species is Apium graveolens L., commonly known as celery, smallage, or wild celery, which is a biennial herb widely cultivated globally for its edible petioles (stalks), leaves, and seeds used in culinary applications. Native to Eurasia, A. graveolens has been utilized since ancient times as a food, flavoring agent, and in traditional medicine for its diuretic, anti-inflammatory, and antioxidant properties, while also serving as animal fodder and, in some contexts, a poison. The genus name Apium derives from the classical Latin term for celery, reflecting its long history in Roman agriculture and cuisine.[2][3][4] Other notable species include Apium prostratum Labill., known as sea celery, a perennial herb found in coastal habitats across southern Australia, New Zealand, and southern South America, traditionally harvested for its edible leaves and stems. The genus as a whole exhibits adaptations to moist, marshy environments, with species often growing in coastal or riparian zones, and several have ornamental or minor medicinal uses in their native ranges. Taxonomic studies recognize the genus's diversity mainly in the Southern Hemisphere, though ongoing molecular research continues to refine species boundaries within Apiaceae.[1][5]Taxonomy and etymology
Etymology
The genus name Apium derives from the Latin noun apium, which served as the classical term for celery (Apium graveolens) or parsley-like plants in ancient Roman usage.[6][7] This nomenclature reflects the plant's recognition in antiquity as a member of the umbelliferous family, often associated with marshy environments.[8] The term apium appears prominently in classical texts, such as Pliny the Elder's Natural History (Book 19), where it denotes various marsh-dwelling umbellifers, including celery, valued for their aromatic qualities and habitat preferences.[9][8] Etymologically, apium is believed to originate from the Celtic word apon, meaning "ditch" or "watercourse," alluding to the genus's affinity for wet, aquatic habitats.[10] Some linguistic analyses also link it to Latin apis ("bee"), due to the flowers' attraction to pollinators, though the Celtic derivation better aligns with ecological connotations.[11] This Latin root influenced common names like "celery" across European languages, evolving through Old French céleri from Italian dialects.[12]Taxonomic history
The genus Apium was initially described by Carl Linnaeus in the first edition of Species Plantarum in 1753, where he included two species within the family Apiaceae (then known as Umbelliferae), establishing the modern taxonomic framework for the genus.[1] Linnaeus's treatment focused on basic morphological distinctions, with A. graveolens later designated as the conserved type species.[1] Throughout the 20th century, taxonomic revisions significantly refined the circumscription of Apium, addressing issues of synonymy and generic boundaries amid growing collections from diverse regions. A pivotal contribution came from Mildred E. Mathias and Lincoln Constance in their comprehensive treatment of Umbelliferae for the North American Flora (parts 28B and 28C, 1944–1945), which reduced the number of recognized species through extensive synonymy and transfers to other genera, narrowing the count from over 20 to approximately 12 by consolidating morphologically similar taxa and excluding peripheral elements like sections reassigned to genera such as Niphogeton. Subsequent adjustments, including those by Constance in 1951, further clarified limits by moving Andean species out of Apium. As of 2025, the current circumscription of Apium follows Plants of the World Online, recognizing 12 accepted species based on integrated morphological and molecular phylogenetic data that confirm monophyly within Apiaceae.[1] The genus is classified in tribe Apieae of subfamily Apioideae, a placement supported by nuclear ribosomal ITS and chloroplast sequence analyses highlighting shared fruit and inflorescence traits among included taxa.[13]Description
Morphology
Apium species are annual, biennial, or perennial herbs that are typically glabrous, ranging from robust to slender in form, and exhibit erect, decumbent, or creeping habits, growing to heights of 10–120 cm.[14] The stems are generally branched from the base and supporting the overall structure of the plant.[15] The leaves are pinnate or pinnate-ternate, often ternately decompound, measuring 5–30 cm in length, with sheathing bases at the petioles; they are typically glabrous, though some species may be sparsely pubescent.[14] Upper leaves tend to become sessile, while basal leaves are petiolate.[15] The root system is usually a taproot, though fibrous roots occur in some species, providing anchorage in various substrates.[3] Inflorescences consist of compound umbels, typically 2–10 cm in diameter, with 5–20 rays, often leaf-opposed and sessile or shortly pedunculate; bracts are few or absent, while bracteoles number from few to numerous and may be foliaceous.[15] Flowers are small, 1–2 mm across, hermaphroditic, and white to greenish, featuring five petals that are ovate to suborbicular with an inflexed apex and five sepals with obsolete or very small teeth.[15] Fruits are schizocarps, 1–3 mm long, ovate to elliptic-oblong, glabrous, and laterally compressed, with prominent primary ribs, one oil tube in each furrow (valleculae), and two on the commissure; mericarps bear five longitudinal ribs and four oil ducts in the furrows plus two on the face.[15] Across species, morphological variations include swollen petioles in cultivated forms of Apium graveolens, such as celery.[16]Reproduction
Many Apium species, particularly biennials like A. graveolens, exhibit a life cycle characterized by vegetative growth during the first year, when plants develop a basal rosette of leaves and an extensive root system, followed by reproductive development in the second year after a period of vernalization induced by cold temperatures.[17][18] This pattern applies to biennial species in the genus, though others, like Apium prostratum, display perennial habits in certain habitats. Flowering typically occurs from summer to autumn in the second year, varying by species and latitude, with inflorescences forming as compound umbels that support numerous small, hermaphroditic flowers adapted for insect visitation.[4] Pollination is primarily entomophilous, mediated by insects such as bees, flies, and butterflies, which are attracted to the flowers' nectar and scent; while self-compatible and prone to autogamy due to the protandrous flowering sequence, outcrossing predominates in natural populations to promote genetic diversity.[18][19] Following fertilization, fruits develop as small schizocarps, each comprising two mericarps containing a single seed, which mature over several weeks.[19] Seed dispersal occurs mainly through gravity, with the lightweight, ribbed fruits falling near the parent plant and facilitating self-seeding in suitable microsites; in wetland-adapted species like A. graveolens, hydrochory via water currents can extend dispersal distances, while the fruits' ridged surfaces occasionally enable epizoochory by attaching to animals.[4][20] Propagation in Apium is almost exclusively sexual through seed production, with high viability under optimal conditions but rare vegetative reproduction limited to cultivated selections or species like A. prostratum via root or stem cuttings in favorable environments.[18]Diversity and species
Accepted species
The genus Apium includes 12 accepted species, primarily occurring in temperate and subtropical regions across the Southern Hemisphere, with some extending into the Old World. These species are typically herbaceous, often biennial or perennial, with pinnate or ternate-pinnate leaves, ridged stems, and umbelliferous inflorescences adapted to wetland or coastal environments.[1] The accepted species are as follows:| Species | Authority | Brief traits | Native distribution |
|---|---|---|---|
| Apium annuum | P.S.Short | Annual herb | Southern Australia.[21] |
| Apium australe | Thouars | Perennial herb | Southern South America, subantarctic islands.[22] |
| Apium chilense | Hook. & Arn. | Perennial herb, up to 0.5 m tall | Northern and central Chile, Juan Fernández Islands.[23] |
| Apium commersonii | DC. | Biennial or perennial herb | Argentina to Uruguay.[24] |
| Apium fernandezianum | Johow | Perennial herb | Juan Fernández Islands.[25] |
| Apium graveolens | L. | Biennial herb, up to 1 m tall, with thickened edible leaf stalks | Macaronesia to North Africa, Europe to western Himalaya; widely cultivated.[2] |
| Apium insulare | P.S.Short | Biennial or perennial herb, slender stems | Islands in Bass Strait (Victoria) to Tasmania, Lord Howe Island (Australia).[26] |
| Apium larranagum | M.Hiroe | Perennial herb | Uruguay.[1] |
| Apium panul | (Bertero ex DC.) Reiche | Perennial herb | Chile to western and central Argentina.[27] |
| Apium prostratum | Labill. ex Vent. | Perennial prostrate herb, known as sea celery | Southern Africa, southeastern Australia, New Zealand, Tubuai Islands, Pitcairn Island, Easter Island, southern Brazil to northeastern Argentina.[28] |
| Apium santiagoensis | M.Hiroe | Perennial herb | Chile.[1] |
| Apium sellowianum | H.Wolff | Perennial herb | Bolivia to Brazil and northeastern Argentina.[29] |
Formerly included species
Several species historically classified within the genus Apium L. (Apiaceae) have been reclassified to other genera following molecular phylogenetic analyses conducted from the late 1990s onward. These studies, employing nuclear ribosomal internal transcribed spacer (ITS) regions and chloroplast markers such as rpoC1 intron and trnL-trnF intergenic spacer, demonstrated that the broad circumscription of Apium was polyphyletic, with included taxa forming distinct evolutionary lineages outside the core Apium clade comprising A. graveolens L. and close relatives.[30] A significant reclassification occurred in 2010, when five Eurasian species previously treated as Apium were transferred to the restored genus Helosciadium W.D.J. Koch, based on combined morphological and molecular evidence confirming their monophyly as a sister group to Apium sensu stricto.[30] This revision emphasized differences in fruit anatomy, such as the presence of prominent lateral ribs and vittae patterns in Helosciadium, contrasting with the more uniform ribs and secretory structures in core Apium species. The transferred taxa are primarily wetland herbs, often with prostrate or floating growth forms adapted to aquatic or semi-aquatic environments, unlike the upright, terrestrial habit of many retained Apium species. The key examples include:- Helosciadium nodiflorum (L.) W.D.J. Koch (basionym Apium nodiflorum L.), a creeping perennial of damp meadows and ditches in Europe, distinguished by its pinnatisect leaves and non-rooting nodes.[30]
- Helosciadium repens (Jacq.) W.D.J. Koch (basionym Apium repens (Jacq.) Lag.), a mat-forming herb of coastal saltmarshes, featuring finely dissected leaves and a stoloniferous habit.[30]
- Helosciadium inundatum (L.f.) W.D.J. Koch (basionym Apium inundatum (L.f.) Rchb.), an annual or short-lived perennial of shallow freshwater bodies, with elongated, submerged stems and simple umbels.[30]
- Helosciadium crassipes W.D.J. Koch ex Rchb. (basionym Apium crassipes Waldst. & Kit.), a Mediterranean species of wet habitats, notable for its robust peduncles.[30]
- Helosciadium bermejoi (Carretero, Uribe-Echevarría & Devesa) A.C. Ronse (basionym Apium bermejoi Carretero, Uribe-Echevarría & Devesa), an Iberian endemic of saline habitats, characterized by compact inflorescences and specialized fruit secretory canals.[30]