Caldesia is a small genus of aquatic plants in the family Alismataceae (order Alismatales), comprising three living species distributed across Europe, Asia, Africa, and Australia. Plants are rooted emergent or floating aquatics with leaves borne entirely in a basal rosette; the blades are ovate to elliptical with a cordate or subcordate base and may float on the water surface or stand upright as aerial leaves. Flowers are hermaphrodite, arranged in racemes or panicles, and bear six to eleven stamens; the carpels are few to numerous, arranged in a single free whorl, each containing a single ovule with a subventral style. The fruit is a small drupe with a woody endocarp and spongy, often swollen exocarp that may be smooth, tuberculate, or spiny — features that aid water dispersal.
The genus has a notably rich fossil record, with material spanning the Oligocene through the Pleistocene in Eurasia, and fossil species also described from Idaho and Vermont in North America; ten fossil species have been named in total. The most widespread living member is Caldesia parnassifolia, which occurs across much of Europe, temperate and tropical Asia, Africa, and Queensland. Caldesia grandis is restricted to Assam, Bangladesh, and southern China, while Caldesia oligococca and its varieties range across tropical Australia, western Africa, and parts of South and Southeast Asia.
The genus was formally circumscribed by the Italian botanist Filippo Parlatore in 1860 (Flora Italica, vol. 3) and named in honour of Ludovico (Luigi) Caldesi (1821–1884), an Italian politician and naturalist.
Etymology
The genus name Caldesia honours Ludovico (Luigi) Caldesi (1821–1884), an Italian politician and botanist. The genus was formally described by Filippo Parlatore in 1860 in Flora Italica, vol. 3.
Distribution
The three living species of Caldesia are collectively distributed across Europe, Asia, Africa, and Australia. Caldesia parnassifolia is the most wide-ranging, occurring from Europe through temperate and tropical Asia, Africa, and Queensland. Caldesia grandis is confined to Assam, Bangladesh, and southern China, while Caldesia oligococca and its varieties span tropical Australia, western Africa (Mali to Chad), and parts of South and Southeast Asia including India, Pakistan, Sri Lanka, Thailand, Vietnam, and Java. The genus also has an extensive fossil record in Eurasia (Oligocene–Pleistocene) and North America.
Ecology
Caldesia species are rooted aquatic or semi-aquatic plants of shallow freshwater habitats, typically growing in ponds, marshes, slow-moving rivers, and flooded rice paddies. The spongy exocarp of the fruit facilitates dispersal by water (hydrochory). Plants produce both floating and aerial leaf forms depending on water depth and conditions.
Taxonomy Notes
The genus was circumscribed by Filippo Parlatore in 1860 and belongs to the family Alismataceae within the order Alismatales. Caldesia parnassifolia has been treated under the synonym Caldesia reniformis (D.Don) Makino. Ten fossil species have been described; the genus's fossil record stretches from the Oligocene through the Pleistocene in Eurasia, with additional fossil material known from North America (Idaho and Vermont).
