Family: CABOMBACEAE

Reference
Family
Genus
Species
Rhizomes monopodial; alkaloids 0; stem with two pairs of vascular bundles, protoxylem lacunae + [see below]; internodes long; petiole with one bundle pair; lamina peltate; inflorescences sympodial (in part); pedicel with 3 bundle pairs; flowers rather small, parts whorled, (2)3(4)-merous, polysymmetric [hexamerous]; P = two whorls of T, C-like, all members with single trace; filaments moderately slender; tapetum more or less amoeboid; pollen endexine lamellate when young, not when mature; pollen tube growth intra-gynoecial; when G 3 or more, inner whorl of three opposite inner P, three vascular bundles equidistant, stylulus +, short, stigma papillate; extragynoecial compitum at least initially 0; ovules 1-3(-5)/carpel, attached variously, outer integument semi-annular [hood-shaped], hypostase +; hilum and micropyle sharing same opening in center of operculum; micropylar endosperm cell with free-nuclear divisions [endosperm helobial]; x = 7 (?8, ?6), nuclear genome [1 C] (0.036-)1.989(-109.219) pg; seedling erect, internodes short [= short shoot of sorts].

Genus 1. Cabomba

Rhizomes from erect short shoots or other rhizomes; vascular plexus at nodes, stomata [on floating leaves] parallel to the veins; short shoots with cataphylls, submerged leaves opposite or 3-whorled, lamina deeply palmately (subdichotomously) dissected, lobes linear; flowering shoots long shoots, from erect shoots or rhizomes, monopodial (becoming sympodial); flowers initially axillary; T in a single whorl, inner T somewhat delayed in development, nectaries +, trichomatous; A 3 [opposite inner T], 6 [alternating with T], extrorse; pollen trichotomocolpate, tectum continuous, striate; G 1-4(-7), (basally connate), style becoming hollow [lysigenous], stigma capitate; fruit follicular; seeds 2-3, spiny; n = 13.

Genus 2. Brasenia

Rhizomes from seedling-derived short shoots; root stele 6-8-arch; vascular bundles bicollateral with central protoxylem lacuna, each surrounded by an endodermis glandular hairs 3-celled; stems encased in thick layer of mucilage, paired, glandular patches at nodes; "lateral bud opposite to the leaf"; flowering shoots short shoots, from rhizomes, sympodial; pedicel often with 3 bundles; T whorls somewhat different in size; A many, outer alternating with T, inner with variable position; pollen scabrate; G 4-18, stigma elongate; fruit achenial, 1-2-seeded; testa cells tall, thick-walled; n = 40.
Cabombaceae are rather small-flowered waterlilies with few ovules or seeds in each carpel; they have floating stems and all the flower parts are free.
Evolution: Pollination Biology & Seed Dispersal. Brasenia is wind pollinated, while Cabomba has paired nectaries (trichome patches) on its inner tepals and is pollinated by flies. M. L. Taylor and Williams (2009) describe details of reproduction of Cabomba from pollination to fertilization, while E. L. Schneider and Jeter (1982) discuss its pollination. For more details, see Erbar (2014) and Gottsberger (2016)
Chemistry, Morphology, etc.. The root endodermis has a Casparian strip and suberin lamellae. The two bundles that share protoxylem lacunae are adjacent vascular bundles in Cabomba but members of opposite pairs in Brasenia (Moseley et al. 1984; C. Yang et al. 2019). The "vessels" in the roots and rhizomes of Cabomba have helical thickenings that are not developed away from the end plate (E. L. Schneider & Carlquist 1996). It is unclear how to interpret nodal anatomy. In Cambomba a trace leaves from each member of a vascular bundle pair which shortly thereafter fuse commissurally, creating a nodal plexus; the foliar traces fuse and then divide, providing two petiolar bundles (Moseley et al. 1984); Schneider et al. (2003) suggest that the axillary bud in Brasenia is on the opposite side of the stem from the leaf that subtends. The peltate leaves are spirally arranged, although in some taxa they are uncommon, while the more or less dichotomously-divided submerged leaves are opposite; for leaf morphology, see Rutishauser and Sattler (1987).
Schneider et al. (2003: p. S287) described the nodal organisation of Brasenia as follows: "a leaf and lateral shoot bud [are] in opposite positions, with the flower to one side at the same node", perhaps consistent was a basically sympodial organization. There are often five vascular bundles in the sepals and three vascular bundles in the petals of Cambomba, in both cases a single trace leaves the floral axis (Moseley et al. 1984). Stamens are sometimes physically close to each nectary and then they appear paired (?rgaard et al. 1992). Pollen of Cabomba has striate exine; although the endexine of mature pollen of Brasenia schreberi is not lamellate, it is laid down in plates (M. L. Taylor & Osborn 2006).
The granular infratectum of the pollen of Podostemaceae has been compared with that of Cabombaceae; both are aquatics (Passarelli et al. 2002).
Some information is taken from Raciborski (1894a, b), Moseley et al. (1984: esp. tables 4, 5) and Williamson and Schneider (1993), both general, Richardson (1969: development of Brasenia flowers), Ito (1986a: floral morphology/anatomy), Erbar (2014) and T?lke et al. (2019), both nectaries, Khanna (1965) and Batygina et al. (1982), both embryology, Floyd and Friedman (2000: endosperm development), and M. L. Taylor et al. (2008: esp. pollen).
Cabomba species list
Data source


Name Author Protologue
Cabomba aquatica Aubl. Hist. Pl. Guiane 1: 321 (1775)
Cabomba caroliniana A.Gray Ann. Lyceum Nat. Hist. New York 4: 47 (1837)
Cabomba furcata Schult. & Schult.f. Syst. Veg. 7: 1379 (1830)
Cabomba haynesii Wiersema Ann. Missouri Bot. Gard. 76: 1167 (1989)
Cabomba palaeformis Fassett Castanea 18: 127 (1953)
Cabomba schwartzii Rataj Acta Amazonica 7: 143 (1977)
Brasenia species list
Data source
Name Author Protologue
Brasenia Schreberi J.F.Gmel.