Covered Scale by This but Are Never Connate with It
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A synopsis of the Lemnaceae C. den Hartog and F. van der Plas Summary The family Lemnaceae is divided into 2 subfamilies, Lemnoideae with the genera Spirodela and Lemna — Lemna — the latter with 2 subgenera, and Staurogeton and Wolffioideae with the genera Wolffia, Wolffiella, Wolffiopsis, and Pseudowolffia, the last two being new and based on former infrageneric taxa. All these their taxa are described, and types indicated; keys are provided for their distinction. listed with their few reduced. There Recognized species names are synonyms, a being newly are 5 new A of is excluded specific combinations. list invalid and dubious names added. The names are listed separately. An is in is explanatory glossary given ofthe terminologyused the descriptions, and illustrated by some diagrams (fig. 1). Introduction The Lemnaceae is well-defined and its delineation has diffi- a family never given any The of the within the has been elaborated culty. systematic arrangement genera family by Schleiden (Linnaea 13, 1839, p. 385—392; Beitr. Bot. 1, 1844, p. 229—235) and later by Hegelmaier (Lemnac., 1868, p. 1—169; Bot. Jahrb. 21, 1895, p. 268—305). In his last work Hegelmaier recognized 4 genera: Spirodela, Lemna, Wolffia, and Wolffiella. Hegel- work has been almost for the fact maier's accepted generally, except that most British Bentham & Hooker authors, following (Gen. Pi. 3, 1881, p. 1000—1001) have not In since recognized Spirodela as an independent genus. the years the publication of Hegel- of the has increased maier's work knowledge Lemnaceae considerably. Several new species have been described and and material has become available of flowering fruiting quite a number of species. The need for a new critical revision of the family has been felt for some time, not in the least by physiologists who use these small, readily multiplying plants more and more for their experiments (Hillman, Bot. Rev. 27, 1961, p. 221—287). Recently Daubs (Monogr. in 'a Lemnac., 1965, p. 1—118) published a monograph of the Lemnaceae, order to give critical review of the family in the light of this later knowledge'. Unfortunately this work does the which from not meet requirements can be reasonably demanded a mono- and it well received American graph. consequently was not very (reviews by Howard, Clark Sida and Scientist 54, 1966, p. 242A—243A; & Thieret, 2, 1966, p. 437—438, it examine den Hartog, Blumea 15, 1967, p. 575—576). However, certainly inspired us to of within the and critically the status the various genera family, not to take anything for granted. The results of our studies are with those of taxonomic only partly in agreement the with the earlier authors. We agree division of the Lemnaceae into 2 subfamilies, the Lem- viz. Lemna noideae and the Wolffioideae. Within the Lemnoideae we recognize 2 genera, and Spirodela, as most other authors have done before. In the subfamily Wolffioideae, viz. however, we recognize 4 genera, Wolffia, Wolffiella, Pseudowolffia, and Wolffiopsis. The last-mentioned are the of 2 genera newly described; in original system Hegelmaier BLUMEA No. 356 VOL. XVIII, 2, 1970 Lemnaceae. — A-B. Fig. 1. Diagrams showing the external morphology of Spirodelapolyrhiza (L.) Schlei- A. den; dorsal side of the frond,B. ventral side of the frond. — C. Wolffia sp. (a. stipe; b. budding pouch; d. h. c. node; young frond showing the dorsal scale; e. ventral scale; f. primary root; g. secondary root; i. with male and female root sheath; root cap; j. flowering cavity flower). they figure as sections or subsections. In our opinion they are sufficiently distinct to be regarded as separate genera. this the taxa above the rank of are described. Under each In paper only species genus or subgenus description an annotated list of the species with their full synonymy is given. TERMINOLOGY The Lemnaceae are morphologically very reduced plants, and consequently the terms of the least used in the descriptions various taxa are, at partly, rather different from those the of familiar generally used for description more looking angiosperms. Therefore, for the sake of convenience we have added a list of terms generally used for the description of Lemnaceae, and some diagrams (fig. i). In this paper these terms are used exclusively for descriptive purposes. lacunous under the Air spaces. Large spaces epidermis, filled with gas (or water). Budding pouch. The basal cavity in the Wolffioideae and the two lateral pockets in the Lemnoideae called here the fronds the are budding pouches, as young are produced. In Lemnoideae one of the two pouches can also give rise to an inflorescence and is then often called a The of the reproductive pouch. budding pouch Wolffioideae never pro- duces an inflorescence. Dorsal scale. A small, almost round, membranous scale at the base of the dorsal side of a young frond of Spirodela, disappearing with age. F. A Lemnaceae C. den Hartog & van DER Plas: synopsis of the 357 Druses. Asteroid crystals of Ca-oxalate in the parenchyma of Spirodela. Flowering cavity. A dorsal cavity in the frond of the Wolffioideae in which the inflorescence is formed. This cavity is formed just before the frond flowers. Frond. A single plant of a Lemnacea. Node. Point on the frond from which the roots descend. One vascular bundle connects the the from node stipe with node; the I or more nerves proceed towards the apex. Petiole. See stipe. cells. to Solereder & Anat. Monokot. Pigment According Meyer (System. 3, 1928, p. the brown cells cells and the red 170—175) pigment are myriophyllin pigment cells contain anthocyanin. Roots which the ventral scale and whose sheaths Primary roots. perforate are grown together with that scale. Theseroots are appearing at an earlier stagein the development the frond than visible in of the secondary roots, and are already very young fronds (Spirodela). Prophyllum. See ventral scale. Raphides. Needle-like crystals of Ca-oxalate arranged in bundles (Lemnoideae). Reproductive pouch. See budding pouch. A frond of Resting bud. consisting a very compact tissue, filled with reserve food, sinking to the bottom in winter and rising to the surface in spring (winter bud!). In temporary kind ofbuds the waters the same are formed, enabling the species to survive dry period. The turion of Spirodela is a special form of a resting bud. sheath the of Root cap. A cylindrical membranous surrounding tip the root, cohering of the with the root sheath at an early stage in the development root. Root scale. See ventral scale. Root sheath. A cylindrical membranous sheath surrounding the base of the root, cohering with the at the ofthe the the root cap an early stage in development root. As root grows two parts become separated. Secondary roots. Roots which do not perforate the ventral scale, their sheaths are covered scale by this but are never connate with it. These roots appear at a later stage in the development of the frond than the primary roots (Spirodela). Stalk. See stipe. stolon-like which the attached the mother Stipe. A structure by young plant is to plant. It is often fugacious. Although it is certainly not homologous with the stalk of a leaf it is often referred to as a petiole. Turion (in Spirodela polyrhiza). A young frond differing from normal fronds by its thicker habit and with The more compact tissue filled reserve food. dorsal as well as the ventral scale and In it sinks the some root primordia are present. autumn to bottom, and the surface in spring it rises to again. of Ventral scale. A scale at the ventral side of the frondof Spirodela, covering the bases the with secondary roots and/or grown together the root sheaths of the primary roots. Winter bud. See resting bud. LEMNACEAE Monoecious, very rarely dioecious, small to minute aquatic annuals, floating at the surface of the of water, or floating just below the surface whereby only a very small part the frond is exposed to the air, or completely submerged and then rising to the surface in the small short flowering period. Fronds either solitary or connected in groups by hyaline flat or rarely elongate green stipes, symmetric or asymmetric, or inflated, ranging in 358 BLUMEA VOL. XVIII, No. 2, 1970 shape from reniform, round, elliptic, lanceolate, and linear to globose, green, with or red brown with both of without or pigment cells, sometimes types pigment. Roots when there is there is several, one, or none. Budding pouches I or 2; one budding pouch this inflorescence one flowering cavity and in a spatheless is borne (an exception is Wolffi- has when there of these opsis which 2 flowering cavities); are 2 budding pouches one gives rise to an inflorescence surrounded by a spathe. Inflorescence consisting of i female male flowers. of anther and i or 2 Perianth none. Male flower consisting a single stamen; uni- or bilocular. Femaleflower inserted above the male fiower(s), consisting of I sessile, unilocular with a short Ovula a seeded utricle. globular, ovary style. 1—4. Fruit 1—4 Seeds ribbed or smooth. KEY TO THE SUBFAMILIES Roots lateral, of axis. I. present. Buddingpouches 2, basal, oneoneither side the Inflorescence 1,developing from the one of budding pouches, consisting of 1 female and 2 male flowers enclosed by a membranous spathe. Anther bilocular, transversely dehiscent. Raphides present Lemnoideae rise 1. Roots none. Budding pouch 1, basal, median, never giving to an inflorescence. Inflorescence 1 Anther (rarely 2), dorsal, consisting ofa cavity containing1 female and 1 male flower, without a spathe. unilocular, apically dehiscent. Raphides none Wolffioideae SUBFAMILY LEMNOIDEAE Smallwater plants, floating at the surface or sometimes completely submerged in which case they come to the surface only in the flowering period.