Asparagus is a large genus of perennial flowering plants in the family Asparagaceae (subfamily Asparagoideae, order Asparagales). Plants of the World Online accepts roughly 211 species, distributed natively from Europe and across Africa eastward through the Middle East and southern Asia to northern Australia, with strong centres of diversity in the Mediterranean basin and southern Africa. The genus was formally established by Linnaeus in Species Plantarum (1753), with the authorship cited as Tourn. ex L. in modern checklists.
The most striking morphological feature of the genus is that the visible "foliage" is not made of true leaves at all. True leaves are reduced to small membranous scales; the photosynthetic work is done by needle- or strap-shaped modified stem branches called cladodes (or phylloclades) that arise in tufts from the scale axils. This produces the feathery or fern-like appearance familiar from ornamental species such as A. setaceus and A. densiflorus, as well as the mature growth of the edible A. officinalis once its spears expand.
Most species are dioecious, with separate male and female plants, though hermaphrodite flowers occur occasionally. The flowers themselves are small and bell-shaped, typically greenish-white to yellowish, and are followed by small fleshy berries that ripen red (or sometimes black). These berries are toxic to humans, although they are eaten and dispersed by birds. Below ground, the plants grow from a fleshy adventitious root system known as a crown, which allows them to overwinter and to resprout vigorously each spring.
The genus is best known in cultivation for a handful of species. A. officinalis, garden asparagus, has been grown as a spring vegetable since at least Roman times, with young shoots harvested as they emerge from the crown. Several southern African species — notably A. setaceus, A. densiflorus and A. aethiopicus — are popular houseplants and ornamental "asparagus ferns", grown for the airy texture of their cladodes rather than for their edibility. A. racemosus (shatavari) is widely used in Ayurvedic medicine in South Asia, and A. acutifolius is gathered as wild asparagus around the Mediterranean.
The same vigour that makes ornamental Asparagus species easy to grow has also made several of them serious environmental weeds. A. asparagoides (bridal creeper) is listed among Australia's twenty Weeds of National Significance and is a declared unwanted organism in New Zealand, having escaped from horticultural plantings to smother native vegetation with dense foliage and thick mats of underground tubers.
Etymology
The genus name Asparagus comes directly from classical Latin asparagus, itself borrowed from Ancient Greek aspáragos. In English the word was for a long time corrupted by folk etymology into "sparrow grass", a form that persisted in rural usage well into the nineteenth century before "asparagus" was re-established as the standard name.
Distribution
The native range of Asparagus is exceptionally broad. Plants of the World Online maps the genus across Europe, the Mediterranean, sub-Saharan and southern Africa, the Middle East, Central and South Asia, China, Japan, parts of southeast Asia, Madagascar and northern Australia, with TDWG records from dozens of countries on every Old World continent. Switzerland's national checklist (Info Flora), for example, records two species — A. officinalis and A. tenuifolius — at its temperate northern edge. Through cultivation the genus has been introduced and widely naturalised across the Americas from Canada to Argentina, in Australasia and the Pacific, across the Caribbean, and into parts of northern Europe.
Taxonomy
Asparagus was established by Linnaeus in Species Plantarum (1753), and is conventionally cited as Asparagus Tourn. ex L. in modern checklists. Plants of the World Online and GBIF agree on its placement in family Asparagaceae, subfamily Asparagoideae, within order Asparagales. POWO currently accepts 211 species in the genus.
Cultivation
Across the genus, Asparagus species are easy garden subjects, generally tolerant of any good soil with a preference for rich, well-drained sandy loam, and indifferent to mildly acid, neutral or mildly alkaline pH. The same broad tolerance — light sandy, medium loamy or heavy clay soils — applies to many of the ornamental species. The crowns are perennial and resprout from below ground each spring, which is what makes A. officinalis suitable for long-lived vegetable beds harvested for fresh spring spears.
Cultural uses
Several Asparagus species have significant culinary or medicinal traditions. A. officinalis, garden asparagus, has been eaten as a spring vegetable in Europe and the Mediterranean since Roman and Byzantine times. A. acutifolius is still gathered as wild asparagus around the Mediterranean, and A. racemosus — shatavari — is a major medicinal plant in South Asian (especially Ayurvedic) practice. Note that the red berries produced by many species are toxic to humans even where the young shoots are edible.
Conservation
The conservation story for Asparagus is unusual in that the genus's main risk to ecosystems is one of invasion rather than loss. A. asparagoides (bridal creeper), introduced to Australia from around 1857 for use in floral arrangements, has escaped cultivation so successfully that it is listed among Australia's twenty Weeds of National Significance and is classed as an unwanted organism in New Zealand under the National Pest Plant Accord; it has also naturalised in southern California. It smothers native vegetation with dense above-ground foliage and a thick underground mat of tubers that prevents other species from establishing roots, and its bird-dispersed seeds spread it readily into bushland.
