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Meristic and Organogenetic Variation in Ruppia Occidentalis and R University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications in the Biological Sciences Papers in the Biological Sciences 1993 Meristic and Organogenetic Variation in Ruppia occidentalis and R. maritima Robert B. Kaul University of Nebraska-Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/bioscifacpub Part of the Biology Commons, and the Botany Commons Kaul, Robert B., "Meristic and Organogenetic Variation in Ruppia occidentalis and R. maritima" (1993). Faculty Publications in the Biological Sciences. 854. https://digitalcommons.unl.edu/bioscifacpub/854 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications in the Biological Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Int. J. Plant Sci. 154(3):416-424. 1993. ? 1993 by The University of Chicago. All rights reserved. 1058-5893/93/5403-0007$02.00 MERISTIC AND ORGANOGENETIC VARIATION IN RUPPIA OCCIDENTALIS AND R. MARITIMA ROBERT B. KAUL1 School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588-0118 Floral meristic and organogenetic variation was sampled in Ruppia occidentalis from an alkaline lake of the Nebraska Sandhills and in Ruppia maritima var. rostrata from a saline, non-Sandhills lake nearby. The androecium is meristically stable, always having two stamens, but the gynoecium is not. Seventy- two percent of the flowers of R. maritima had four carpels and the others had three, and in 80% of inflorescences the two flowers had the same number. In about one-third of inflorescences having dissimilar carpel numbers, the four-carpellate flower was uppermost. The number of carpels in each flower of R. occidentalis ranged from four to nine, averaging six, and in 57% of inflorescences both flowers had the same number; of those that did not, most had more in the lower than upper flower. Twenty-five percent of the flowers had four carpels, 8% had five, 35% had six, 15% had seven, 14% had eight, and 3% had nine. Ordered, dimerous, decussate organogenesis through the first four carpels followed the same pattern in both species, but carpels beyond four were alternate with the first four and the decussate pattern was broken. The stomatiferous dorsal lobe of each carpel produced persistent gas bubbles that probably aid flotation of the inflorescence and might function in trapping pollen as well. Only ephydrophilous polli- nation was observed in both species. Introduction so many other hydrophilous aquatic plants, prob- ably belies its ancestral complexity, but the Alis- While all species of Ruppia have just two flow- matiflorae have a mosaic of ancestral and derived ers in each inflorescence and two stamens in each character states, and thus a clear phylogeny of flower, there is gynoecial meristic variation with- Ruppia and its close relatives is not yet available. in and among species and even between flowers Dahlgren and Rasmussen (1983) regarded as ple- in the same inflorescence. A tetramerous gynoe- siomorphic in the monocotyledons the perfect cium is common in the cosmopolitan Ruppia tricarpellate tepal-bearing flower having six sta- maritima L., but dimery, trimery, and pentamery mens in two whorls of three. are known (Posluszny and Sattler 1974b; Jacobs The homology of the flower of Ruppia and its and Brock 1982). Ruppia tuberosa Davis and tepals, apparent outgrowths of its stamen con- Tomlinson, Ruppia polycarpa Mason, and Rup- nectives, have been debated; the various inter- pia megacarpa Mason in Australia have two to pretations were reviewedby Singh (1965), Burger 19, four to 16, and two to seven carpels in each (1977), and Posluszny and Sattler (1974b). Less flower, respectively (Brock 1982; Jacobs and attention has been given to the nature of the gy- Brock 1982). In New Zealand, R. polycarpa has noecium, and here I present observations on gy- two to 16 carpels and R. megacarpa usually has noecial meristic variation and floral and fruit or- four, but the upper flower in its inflorescence ganogenesis and function in two species, including sometimes has five or six (Mason 1967; Jacobs a variety of the North American interior, con- and Brock 1982). centrating on aspects not published elsewhere for Ruppia is often given its own family, Ruppi- Ruppia. aceae, or is placed with Potamogeton and Groen- Floral anatomy is known for Ruppia from the landia in Potamogetonaceae. Recent classifica- Mediterranean coast of France (Roze 1894), from tions put it in -monocotyledon subclass Minnesota (Singh 1965) and coastal Connecticut Alismatidae (Cronquist 1981) or superorder Alis- (Graves 1908), and from the interior of Argentina matiflorae (Dahlgren and Rasmussen 1983). Cla- (Gamerro 1968). Some aspects of floral devel- distic analysis of the Alismatiflorae by Dahlgren opment of R. maritima are published for speci- and Rasmussen (1983) showed Potamogetona- mens from coastal waters in France (Roze 1894) ceae (including Ruppia) and the marine families and Connecticut (Graves 1908) and, in detail, Posidoniaceae and Zosteraceae to be synapo- from New Brunswick, Canada (Posluszny and morphic and strongly derived. Those authors Sattler 1974b), but none is published from inte- urged caution in interpreting the cladogram be- rior waters or for other species. cause of convergent evolution. The relatively simple floral morphology of Ruppia, like that of Material and methods I collected Ruppia occidentalis S. Watson from 1 Reprints available from the author. Big Alkali Lake in Cherry County, Nebraska, be- Manuscript received January 1993; revised manuscript re- tween high dunes of the Sandhills. The lake and ceived April 1993. others nearby have growing-season pH 9-10.3, 416 KAUL-RUPPIA FLOWERS 417 total alkalinity (carbonates) of 700-34,000 mg/ Table 1 L, and Na+ + K+ of 700-2,200 mg/L. I gathered CARPEL NUMBERS IN FLOWERS AND NFLORESCENCES Ruppia maritima L. var. rostrata Agardh from saline Oak Lake in Lancaster County, Nebraska, Ruppia maritima var. outside the Sandhills; the lake has a mud bottom, rostrata Ruppia occidentalis growing-season pH > 9.5, fewer carbonates (ca. No. of No. of 265 mg/L), and Na+ + K; of ca. 1,1 00 mg/L Carpels per nfl Carpels per io- flower in flower in (Kaul 1992). 1 grew transplanted flowering plants inflorescences es infloresences of both species in tapwater in the laboratory un- _ cences cences der fluorescent lights where, for 3 wk, they pro- Lower Upper (N Lower Upper (N duced foliage and flowers that liberated pollen. flower flower = 96) flower Rower = 96) The species reported on are readily separable using floral and vegetative characters (Kaul 1992) 3 3 17 4 4 24 and are ecologically segregated, as noted above. 3 4 6 5 5 6 4 3 13 5 7 3 Ruppia occidentalis in the Sandhills has stamens 4 4 60 6 6 17 about 1 mm wide; four to nine carpels; fruiting 7 6 19 peduncles long and strongly coiled; fruits 1.8-3 7 7 3 mm x 1.6-2.4 mm; and two prominent elliptic 8 6 14 8 8 4 white soft spots on the hard black endocarp. In 8 9 3 my specimens -of R. maritima, the stamens are 9 8 2 ca. 0.6 mm wide; the carpels number three or 9 9 1 four; the short fruiting peduncles are uncoiled; X...... 3.76 3.69 6.22 5.80 the fruits are 1.2-1.9 mm x 1-1.3 mm; and the r ........ .52 .82 2xx2 ...... .087. 6.29 62 endocarp spots are nearly circular. The leaves of df 1 1 R. maritima and R. occidentalis are, respectively, P ..... NS <.025 acute and obtuse, denticulate and entire, flattened Overall X 3.72 5.95 and terete, and unspotted and red-spotted; and s .... .45 1.46 2...... 6.02 76 the fruiting peduncles of the two species are df 1.... 5 straight and coiled, respectively. P .... <.025 <.00 1 Specimens were dissected and examined living and after fixation in 70% formalin-propionic acid-ethanol (FPA). Specimens for scanning elec- MERISTIC VARIATION tron microscopy were dehydrated in a series to absolute ethanol, critical-point dried, and sput- The number (two) and position (6 and 12 ter-coated for 5 min with gold-palladium. Those o'clock) of stamens was unvarying in all speci- for light microscopy were stained with fuchsin mens of both species I examined, irrespective of and sectioned in paraffin-plastic. the number and position of carpels. Occasional The flowers are described as seen in polar view flowers had undehisced anthers that were full- while attached on the sides of the inflorescence sized but collapsed and empty of pollen (fig. 2F). rachis, its distal end uppermost. Thus, each flow- In most such specimens, both flowers of the in- er has an "upper" and "lower"9 half and its ap florescence had barren anthers, but the carpels pendages occur in positions easily described using were fertile. hours of the clockface. There was variation in number of carpels with- in and between inflorescences (table 1). In my Observations collection, 72% ofthe flowers of Ruppia maritima had four camels (fig. ID, E) and all others had ORGANOGRAPHY three (fig. IF). In 80% of the inflorescences, both In both species, the vegetative phyllotaxy is flowers had the same number of carpels, and 22% distichous and the shoot system becomes sym- and 78% of those flowers had three and four car- podial when the first inflorescence primordium pels, respectively. In the other 20% of inflores- appears. A renewal shoot arises immediately be- cences, one flower had four camels and the other low each inflorescence and eventually terminates had three, and the four-carpellate flower was up- in an inflorescence. Each inflorescence has two permost on the rachis in about one-third of them flowers, neither subtended by a bract, one 1800 (table 1).
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