Takhtajan Armen. Flowering Plants

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594 Class LILIOPSIDA

Weber A. 1980. Die Homologie des Perigons der Zingiberaceen:

Ein Beitrag zur Morphologic und Phylogenie des

Monocotylen-Perigons. Plant Syst. Evol. 133: 149–179.

Williams CA, JB Harborne, and B Mathew. 1988. A chemical

appraisal via leaf ﬂ avonoids of Dahlgren’s Liliiﬂ orae.

Phytochemistry 27: 2609–2629.

Wilson KL and DA Morison, eds. 2000. Monocots: systematics

and evolution. CSIRO, Collingwood.

Yeo PE. 1989. What is happening to the monocotyledons? Plant

Syst. Evol. 167: 75–86.

Zavada M. 1983. Comparative morphology of monocot pollen

and evolutionary trends of apertures and wall structures. Bot.

Rev. 49: 331–379.

Zimmerman MH and PB Tomlinson. 1972. The vascular

system of Monocotyledonous stems. Bot. Gaz. 133:

141–155.

A. Takhtajan, Flowering Plants, 595

Aquatic or marsh herbs. Leaves alternate or less often

opposite or verticillate, with parallel or arcuate vena-

tion, usually with vaginate base. Stems with axillary,

multiseriate hairs (intravaginal squamules) at the

nodes (replaced by uniseriate, threadlike hairs in

Scheuchzeria). Vessels absent or only in roots. Flowers

in various types of inﬂ orescences or solitary, bisexual

or unisexual, actinomorphic or zygomorphic. Tapetum

always plasmodial. Pollen grains almost always

3-celled, 1-colpate or inaperturate, less often pantopo-

rate. Gynoecium apocarpous or syncarpous (mostly

paracarpous), sometimes pseudomonomerous. Ovules

bitegmic, crassinucellate, or sometimes almost tenui-

nucellate. Endosperm helobial or less often nuclear.

Fruits of various types, in most archaic members mul-

tifollicles. Seeds usually without endosperm or some-

times only with vestigial endosperm.

Alismatidae share a common origin with Liliidae

and some genera (e.g. Toﬁ eldia) occupied the some-

what intermediate position.

Alismatidae are one of the most archaic groups of

monocotyledons. However, they are one of the blind

branches of the archaic liliopsids rather than a basal,

ancestral group (Les and Haynes 1995; Takhtajan

1997). They are extremely heterobathmic and in

general very specialized. Cladistically the Alismatidae

are very diversiﬁ ed and consist of fairly isolated

groups, which I prefer to consider as separate orders

(Takhtajan 1987).

Derived from some archaic herbaceous members of

early liliopsids.

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Subclass I. ALISMATIDAE

596 Subclass I. ALISMATIDAE

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Superorder PETROSAVIANAE

Order 1. PETROSAVIALES

Small, chlorophyllous or achlorophyllous, rhizoma-

tous herbs with slender, usually simple, erect to creep-

ing stems; stems with a ring of bundles. Calcium

oxalate crystals present (Toﬁ eldiaceae) or absent.

Raphides absent or present. Vascular system weakly

developed, with vascular bundles in singular ring.

Some vessels only in roots, with scalariform perfora-

tions. Sieve-element plastids of P1/2c-type (Behnke

2002). Leaves alternate, spirally arranged, basal or dis-

tichous, linear or reduced to scales, unifacial of bifa-

cial (Japonoliriaceae). Stomata anomocytic. Flowers

small, in terminal or axillary (Japonoliriaceae) corymbs

or racemes, rarely solitary, bracteate, with or without

bracteoles, 3-merous, bisexual, actinomorphic.

Perianth segments of six, in two cycles, persistent, free

or basally connate. Stamens six, in two cycles, free or

adnate to the base of perianth segments; ﬁ laments

subulate; anthers basiﬁ xed or dorsiﬁ xed, introrse or

latrorse, sometimes appendaged, opening longitudi-

nally. Tapetum secretory. Microsporogenesis simulta-

neous. Pollen grains 1-colpate, gemmate or reticulate.

Septal nectaries present. Gynoecium of three, rarely

4–6, carpels; stylodia free or rarely connate into a

style, short, stigma capitate, subcapitate or styles with

decurrent stigma. Ovary superior or semi-inferior, with

numerous or only 4–5 (Japonoliriaceae) ovules in each

carpel. Ovules anatropous to campylotropous, biteg-

mic or very rarely (Toﬁ eldia iridaceae, some sp.

Narthecium) unitegmic, crassinucellate to semicrassi-

nucellate. Female gametophyte of Polygonum-type or

sometimes of Allium-type. Endosperm helobial or

nuclear (Petrosavia). Fruits follicular or capsular,

septicidal or ventrally dehiscent in upper part. Seeds

small, more or less winged, often with appendages,

testal; embryo small to minute and undifferentiated;

endosperm copious, containing oil, proteins, or starch

(Japonolirion). Steroidal saponins and chelidonic acid

present.

Key to Families

1 Plants mycotrophic. Flowers in terminal corymbs or

racemes; anthers dorsiﬁ xed. Small herbs with slen-

der, usually simple, erect stem and thin rhizome

covered with sheathing scale leaves. Roots with a

cortex consisting of 4–6 layers of parenchyma cells

containing mycorrhizal hyphae. Raphide idioblasta

present. Vascular system weakly developed, with

vascular bundles in singular ring. Some vessels in

roots only, with scalariform perforations. Leaves

reduced to alternate scales, the leaf primordial formed

in distichous succession (Stant 1970). Flowers small,

in terminal corymbs or racemes, each subtended by a

well-developed linear bract and bears a small bracte-

ole at the base of the pedicel, bisexual, actinomor-

phic. Perianth of six imbricate, basally connate,

persistent, colorless segments in two cycles, the outer

narrow, the inner broad-ovate, with a small gland at

base. Stamens six in two cycles; ﬁ laments subulate,

adnate to the base of the perianth segments; anthers

ovate, dorsiﬁ xed, introrse, opening longitudinally;

connective very shortly prolonged. Pollen grains

gemmate. Gynoecium of three very shortly basally

connate carpels with sutures closed at anthesis; stylo-

dia short, with slightly biﬁ d, subcapitate stigma;

ovary semi-inferior, with numerous ovules on basal

Superorder PETROSAVIANAE 597

submarginal placentas. Septal nectary present as sep-

tal glands, which extend from just below the lower-

most ovular insertion up to the level of carpellary

separation, where they open on the lateral surfaces of

the carpels and produce nectar drops (Sterling 1978).

Ovules anatropous, bitegmic, semicrassinucellate,

with nucellar cap. Endosperm nuclear. Fruits

recurved-spreading, basally united follicles. Seeds

numerous, minute, brown-ribbed, winged all around,

with minute, undifferentiated embryo consisting of

embryo proper and a suspensor; endosperm copious,

containing oil and protein; seed coat formed by the

outer layer of inner integument. Raphide idioblasts

present; sieve tube plastids also with polygonal pro-

tein crystalloids. n = 15, 30. . . . 2. petrosaviaceae.

1 Plants not mycotrophic.

2 Capsules septicidal.

3 Calcium oxalate crystals lacking. Flowers in

axillary racemes; anthers basiﬁ xed. Inﬂ ores-

cences axillary. Pollen grains gemmate or

reticulate with roundish brochi. Herbs with

slender, short to creeping, scaly rhizome.

Leaves spiral, basal, tufted, bifacial, linear,

with few parallel veins, scabrous on margin,

sometimes longer than scape. Flowers small, in

simple, long axillary racemes, bracteate, with-

out bracteoles, with short pedicels, 3-merous,

bisexual, actinomorphic, without nectaries.

Perianth segments six in two cycles, free, mem-

branous, persistent, outer oblong, inner obovate

to spatulate. Stamens six in two cycles; ﬁ la-

ments subulate; anthers ovate, introrse.

Gynoecium of three carpels, 3-lobed, essen-

tially apocarpous – carpels loosely connected

only with the interdigitating papillae along the

septal faces; stylodia short, recurved, with

decurrent and papillate stigma; ovary usually

with 4–5 ovules per locule; ovules anatropous,

attached to the ovary wall by their micropyles

and completely ﬁ ll the locule (Remizowa et al.

2006a). The septal nectaries are located in the

lower part of ovary. Fruits separate septicidally

through the weakly connate zone between the

follicules (Utech 1984). Seeds small, broadly

elliptical, without appendages; embryo small,

straight; endosperm copious, starchy, weakly

ruminate (Plisko 2004, personal communica-

tion); seed coat 1-layered, n = 12 (three chro-

mosomes long and with subterminal or

submedian constrictions and nine chromosomes

short and with median or submedian constric-

tions – Satô 1942).. . . . . . 1. japonoliriaceae.

3 Calcium oxalate crystals (druses, cuboidal

crystals) present (unique crystalline inclu-

sions, druses, in parenchymatous tissues, and

prismatic crystals in the bundle sheaths

(Ambrose 1980). Perennial herbs with creep-

ing rhizome and simple or branched sympo-

dial stem. Raphides lacking. Roots ﬁ brous.

Vessels only in roots, with scalariform perfo-

rations. Sieve-element plastids with polygonal

crystals. Leaves spirally arranged, mostly

basal, reduced upwards to bracts, laterally ﬂ at-

tened (unifacial), sheathing at base, linear;

venation parallel, sometimes with midrib.

Flowers small, in terminal, sometimes glandu-

lar, racemose inﬂ orescences, rarely

(Harperocallis) solitary, bisexual, actinomor-

phic, pedicillate or sessile, typically subtended

by a bract and a calyx-like involucre (clycu-

lus) of three (occasionally 2, 4, or 0) distinct or

connate bracteoles. Perianth segments six in

two cycles, free, petaloid, persistent, with

outer cycle sometimes slightly wider or longer

than inner. Stamens usually six in two cycles

or (Pleea) nine or rarely 10 or more; ﬁ laments

free, more or less broadened at base; anthers

basiﬁ xed or dorsiﬁ xed, introrse or latrorse,

occasionally with apical appendage, dehiscing

longitudinally. Pollen grains 2-celled, tectate

or semitectate, with two distal colpi, reticulate.

Gynoecium of three (rarely 4–6) carpels,

nearly apocarpous or syncarpous below and

apocarpous above or (Isidrogalvia) totally syn-

carpous, often (Toﬁ eldia, Pleea, Harperocallis)

stipitate (probably a plesiomorphic condition);

stylodia free or (Isidrogalvia) connate into a

style with capitate stigma. Septal nectaries

(basal intercarpellary glands – a unique nectary

type, which may be nonhomologous with the

septal nectaries of other monocots – Utech

1978; Zomlefer 1997) present. Ovules few to

numerous in each carpel or in each locule, ana-

tropous to campylotropous, bitegmic or more

rarely unitegmic (Toﬁ ldia iridaceae), crassinu-

cellate to tenuinucellate (?). The archesporial

cell cuts off a primary parietal cell. Female

gametophyte of Polygonum-type or sometimes

598 Subclass I. ALISMATIDAE

of Allium-type. Endosperm helobial. Fruits

follicular or septicidal capsules. Seeds elliptical

to fusiform, often with terminal appendages on

one or both ends (micropylar and chalazal);

seed coat testal, phytomelan lacking, but in

Toﬁ eldia contains phlobaphene deposits;

embryo small; endosperm copious. Steroidal

saponins, tannins, chelidonic acid, ﬂ avonoids

(kaempferol, quercetin), and sometimes, as in

Toﬁ eldia, also glycosides and alkaloid absent

(L.S. Teslov 2000, personal communication);

n = 15, rarely 14, 16. . . . . . 3. tofieldiaceae.

2 Capsules loculicidal. Perennial herbs with short

or creeping rhizome. Raphides present.

Scattered ﬁ bres present in the phloem. Root

cortex aerenchyma present. Vessels only in

roots, with scalariform perforations. Leaves

mostly basal, spiral, bifacial or unifacial, linear

to ovate, sessile, narrowed to sheathing base,

parallel veined. Flowers small, in terminal

spikes or simple or compound racemes, bracte-

ate and usually bracteolate, 3-merous, bisexual,

actinomorphic. Perianth segments six in two

cycles, petaloid, free or more or less connate

into a tube, adnate to the lower part of ovary,

persistent. Stamens six in two cycles; ﬁ laments

ﬁ liform, inserted at base of perianth segments,

slender, glabrous, or wooly pubescent; anthers

basiﬁ xed to dorsiﬁ xed, linear to cordate-orbicu-

lar, tetrasporangiate, introrse. Pollen grains

ellipsoid, tectate or semitectate, reticulate,

foveolate, or gemmate. Gynoecium of three

united carpels; style with 3-lobed to punctiform

stigma; ovary superior to semi-inferior, 3-locu-

lar or 3-locular below and 1-locular above,

sometimes with septal nectaries. Ovules numer-

ous, anatropous, according to Remizowa et al.

(2006), all species examined ovules bitegmic,

(unitegmic according to Sterling 1979 at least in

Nartheciun), crassinucellate, with parietal cell.

Female gametophyte of Polygonum-type.

Endosperm helobial. Fruits loculicidal capsules

subtended by persistent perianth Seeds ellipsoid

to fusiform, appendaged at both ends

(Narthecium) or without appendages (Aletris).

Accumulate steroidal saponins and sometimes

glycosides and chelidonic acid, no ﬂ avonols. n

= 12, 13 (common), 21, 22, 23, × more probably

7 (Zomlefer 1997).. . . . . . .4. nartheciaceae.

1. JAPONOLIRIACEAE

Takhtajan 1996. 1/1. Serpentine swamps of northern

and central Japan (Hokkaido, Honshu).

Japonolirion

Most probably the basal family in the monocoty-

ledons.

2. PETROSAVIACEAE

Hutchinson 1934. 1/2. Eastern Asia, West Malesia

(Malaya, Borneo).

Petrosavia (including Miyoshia and Protolirion).

Related to the Japonoliriaceae, but differ in

mycotrophic habitus, in having a semi-inferior ovary,

in the structure of the septal nectaries, stigma, number

of ovules, nuclear endosperm, fruits and oily and

protein endosperm.

3. TOFIELDIACEAE

Takhtajan 1995. 4/25. Temperate Eurasia (especially

eastern Asia), North America, South America

(Venezuela, Guyana, Colombia, Ecuador, Peru).

Harperocallis (1) is endemic to Florida, Isidrogalvia

(5) to northern South America.

Harperocallis, Toﬁ eldia, Pleea (sometimes included

in Toﬁ eldia), Isidrogalvia.

The Toﬁ eldiaceae is one of the archaic family,

which has been considered by many authors as the

basal in monocotyledons (Lotsy 1911; Takhtajan 1959,

1966, 1980, 1987, 1997; Eames 1961; Radulescu 1973;

Goldblatt 1995; Tamura 1998).

4. NARTHECIACEAE

E.M. Fries ex J. Bjurzon 1846 (including Lophiolaceae

Nakai 1943). 4/40. Temperate Eurasia to Malesia,

North America, and (monotypic genus Nietneria)

Venezuela and Guyana.

Narthecium, Nietneria, Aletris (including Metan-

arthecium), Lophiola.

Related to the Toﬁ eldiaceae, but stylodia connate

into a style, anthers mostly extrorse, raphides are

present, and capsule loculicidal. No alkaloids are

known.

Superorder ALISMATANAE 599

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Superorder ALISMATANAE

Order 2. HYDROCHARITALES

Perennial or rarely annual, aquatic herbs often with an

elongate rhizome or stolon, frequently partly or wholly

submerged and rarely free-ﬂ oating. Vessels absent or

only in roots, with scalariform (Hydrocharitaceae) or

with simple (Butomaceae) perforations. Leaves radical

or cauline, alternate, sometimes distichous, or opposite

or verticillate, often more or less sheathing or rarely

stipular-expanded at the base, sometimes differentiated

into petiole and lanceolate, elliptic or cordate-ovate

lamina. Stomata usually paracytic or more often

lacking. Flowers from rather large to very small and

600 Subclass I. ALISMATIDAE

inconspicuous, solitary, paired, or in few-ﬂ owered

cymose inﬂ orescences subtended by two distinct or

more or less connate bracts forming a sessile or long-

pedunculate (sometimes spirally twisted) spathe,

bisexual or more often unisexual and dioecious,

actinomorphic or sometimes slightly zygomorphic,

usually 3-merous. Perianth segments free, mostly six

in two cycles or three in one cycle, rarely perianth

absent. Stamens 2–3 to numerous; anthers basiﬁ xed or

dorsiﬁ xed, tetrasporangiate or seldom disporangiate,

opening longitudinally, introrse to generally extrorse.

Tapetum plasmodial. Microsporogenesis successive or

rarely (Aponogetonaceae) simultaneous. Pollen grains

usually 3-celled. Nectaries present or absent.

Gynoecium of (2)3–6 (up to 15–20) united or nearly

free carpels, rarely (Najadaceae) of one carpel; stylodia

often bilobed or biﬁ d, sometimes shortly connate at the

base; stigmas papillate, sometimes (Butomaceae,

Aponogetonaceae) decurrent; ovary superior or

inferior, unilocular, often with more or less deeply

intruded, free carpellary margins. Ovules numerous to

few, or solitary (Najadaceae), anatropous or orthotro-

pous, bitegmic, or rarely (Aponogeton distachyos)

unitegmic, crassinucellate. Female gametophyte of

Polygonum-type. Endosperm helobial or nuclear

(Najadaceae). Fruits submerged, multifollicles, achene-

like, or ﬂ eshy, berrylike, or less often dehiscent. Seeds

usually few to numerous, ellipsoidal to cylindrical or

fusiform, smooth or with highly complex testa;

endosperm absent or rarely scanty; embryo usually

more or less straight, relatively large, with a massive

hypocotyls, rich of starch. Present proanthocyanidins

(cyanidin) n = 6, 7, 8–15.

The Hydrocharitales are the basal group of the

Alismatidae.

Key to Families

1 Vessels absent. Annual or rarely perennial sub-

merged herbs of fresh or brackish water Stems slen-

der, more or less branched, with a much reduced

conducting system. Roots ﬁ brous. Leaves spiral,

sub-opposite (essentially spirodistichous) or

pseudoverticillate, with sheathing base, linear to

linear-lanceolate, 1-veined, the margins serrulate to

denticulate, the apex acute or acuminate, with 1–3

teeth on each side; sheaths open, and commonly

enclosing two tiny, intravaginal squamules. Stomata

lacking. Flowers very small and inconspicuous, axil-

lary, solitary, or in small clusters, unisexual (monoe-

cious or rarely dioecious), hydrophilous (pollination

takes place under water). Male ﬂ owers are subsessile

and consist of a single stamen and mostly subtended

by one or two very thin hyaline envelopes of

unknown origin; the anther subsessile or on a very

short ﬁ lament, tetrasporangiate or rarely with one

microsporangium, opening by an apical slit.

Microsporogenesis successive. Pollen grains

3-celled, globose to ellipsoidal, inaperturate or rarely

slightly 1-colpate (Bolkhovskikh 1983), with thick

intine and very thin exine. Female ﬂ owers are ses-

sile; they are naked and composed of one ovule sur-

rounded by a very thin (two cell layers thick)

transparent carpellary wall. The gynoecium is either

monocarpellary or pseudomonomerous; the stylo-

dium divided some distance from the base into two

stigmatic branches and sometimes into some shorter,

nonstigmatic lobes as well; ovary superior, with one

basal ovule. Ovules anatropous, crassinucellate. A

parietal cell is cut off from the primary archesporial

cell. Female gametophyte usually of Polygonum-

type, rarely bisporic. Endosperm nuclear. Fruits

indehiscent, with the endocarp tightly enclosing the

seed and dehiscing by decay. Seeds fusiform to

elliptic, more or less areolate, without endosperm,

mesotestal; exotesta more or less deeply pitted with

areolae which are arranged in longitudinal rows

embryo cylindrical, straight or rarely slightly curved;

the mesotesta consists of stone cells; the lower peri-

clinal wall of endotegmen tuberculate. n = 6, 7, 8,

17 +. . . . . . . . . . . . . . . . . . . . . . . . . 3. najadaceae.

1 Vessels present only in roots.

2 Vessels with scalariform perforations.

3 Flowers bracteate. Perennial or rarely annual,

fresh-water or salt-water herbs often with an

elongate rhizome or stolon, frequently partly

or wholly submerged and rarely free-ﬂ oating.

Vessels absent or only in roots, with scalari-

form perforations. Leaves radical or cauline,

alternate, sometimes distichous, or opposite

or verticillate, often more or less sheathing or

rarely (as in Hydrocharis) stipular-expanded

at the base, sometimes differentiated into pet-

iole and lanceolate, elliptic or cordate-ovate

lamina, with various kinds of venation; intra-

vaginal scales present, usually 2–10 or more,

or rarely only one in each leaf axil. Stomata

usually paracytic or more often lacking.

Flowers from rather large to very small and

Superorder ALISMATANAE 601

inconspicuous, solitary, paired, or in few-

ﬂ owered cymose inﬂ orescences subtended by

two distinct or more or less connate bracts

forming a sessile or long-pedunculate (some-

times spirally twisted) spathe, bisexual or

more often unisexual and dioecious, actino-

morphic or sometimes slightly zygomorphic,

usually 3-merous. Perianth segments free to

the base, mostly six in two cycles or three in

one cycle, rarely only two; when six the outer

may be sepaloid, green and valvate, and the

inner petaloid, white or variously colored and

imbricate, sometimes with a basal gland,

rarely perianth absent. Stamens numerous to

2–3 (in some plants even to one), when numer-

ous in up to six cycles of three; anthers bas-

iﬁ xed or dorsiﬁ xed, tetrasporangiate or

seldom disporangiate, introrse to extrorse.

Microsporogenesis successive. Pollen grains

usually 3-celled, inaperturate; the exine is

very thin or reduced; pollen transferred

directly from the male ﬂ ower to the female,

through the air, or (in Thalassia and Halophila)

through the water. Gynoecium of (2)3–6 (up

to 15–20) united carpels; stylodia often

bilobed or biﬁ d, sometimes shortly connate at

the base; stigmas papillate; ovary inferior,

unilocular, often with more or less deeply

intruded, free carpellary margins; placenta-

tion laminar-diffuse (ovules scattered over the

surfaces of the partial partitions) or parietal

when the partitions are not intruded. Nectaries,

when present, usually three, rarely more,

borne on the bases of the styles (probably

androecial in origin – Cook 1998). Ovules

numerous to few, anatropous or orthotropous,

bitegmic, crassinucellate, with the parietal

cell usually cut off from the primary arches-

porial cell. Endosperm helobial. Fruits sub-

merged, ﬂ eshy, berrylike, but generally

dehiscent, splitting up irregularly or some-

times (as in some species of Ottelia) regularly.

Seeds few to numerous, ellipsoidal to cylin-

drical or fusiform, smooth or with highly

complex testa; seed coat formed by the outer

integument; endosperm absent or rarely

(Ottelia) scanty; embryo usually more or less

straight, relatively large, with a massive hypo-

cotyl (often with unicellular hairs) and well

developed radicle and in some genera has

several leaves already developed before ger-

mination the lower periclinal wall of the

inner or less often upper layer of the tegmen

more or less tuberculate. n = ? 6, 7–15.

. . . . . . . . . . . . . . . . . 4. hydrocharitaceae.

3 Flowers without bracts. Perennial freshwater

herbs with starch-rich, sympodial, tuberlike

rhizomes or corms, rooted in the substrate.

Articulated laticifers consisting of long cells

containing tannins (proan-thocyanins) or oil

are present in leaves and the inﬂ orescence

axis. Vessels wanting or only in roots, with

scalariform perforations. Leaves all basal,

usually distinctly petiolate, loosely sheathing

at the base, with intravaginal squamules in the

leaf axils; lamina linear to oblong-elliptic,

sometimes fenestrate by loss of the mesophyll

between the veins, submerged or ﬂ oating, usu-

ally with a distinct midrib and one or more

pairs of apically converging parallel or arcuate

primary veins connected by numerous trans-

verse secondary veinlets. Stomata only on the

ﬂ oating laminas, paracytic. Calcium oxalate

crystals are abundant in the mesophyll of ﬂ oat-

ing leaves. Inﬂ orescence is a simple, bifurcate

or sometimes up to ten times forked spike

exerted from the water on a leaﬂ ess scape and

in bud enclosed by a caducous or sometimes

persistent spathelike bract; rarely (Aponogeton

ranunculiﬂ orus) the inﬂ orescence is con-

densed into a few-ﬂ owered pseudanthium.

Flowers usually small, bisexual or sometimes

unisexual and dioecious, actinomorphic or

sometimes zygomorphic, 3-merous, without

bracts. Perianth segments (1-)2(-6), absent in

female ﬂ owers of dioecious species, free, usu-

ally petaloid and mostly persistent. Stamens

free, mostly six in two cycles, but in A. dis-

tachyos 8–16 in several cycles; staminodia

present; ﬁ laments elongate, anthers small, tet-

rasporangiate, extrorse. Microsporogenesis

successive or simultaneous. Pollen grains

3-celled, more or less ellipsoid, 1-colpate,

with long colpi; the tectum perreticulate with

ﬁ ne supratectal spines; the aperture membrane

may bear small spinules or granules.

Gynoecium of (2)3(-9) carpels; carpels nearly

free or more or less basally and adaxially

602 Subclass I. ALISMATIDAE

connate, but separating at maturity, with septal

nectaries; stylodia short, with a ventral stig-

matic groove (stigmas decurrent); in each car-

pel 2–12 basal-submarginal ovules. Ovules

anatropous, bitegmic or rarely (A.distachyos)

unitegmic, crassinucellate; a parietal cell is cut

off from the primary archesporial cell.

Endosperm helobial. Fruits of nearly free folli-

cles. Seeds smooth, ridged or winged, testal,

with straight embryo and without endosperm.

Testa protective or not, endotegmen tanninif-

erous, or undifferentiated and translucent.

Leucoanthocyanins and ﬂ avonols present,

bur C-glycosylﬂ avons absent. n = 8, 12 +.

. . . . . . . . . . . . . . . . . 1. aponogetonaceae.

2 Vessels with simple perforations. Emergent

aquatic perennial herbs with stout, creeping,

monopodial, dorsiventral, aerenchymatous rhi-

zome, rich in starch and provided with scattered

tanniniferous cells containing proanthocyanins.

Vessels only in the roots, with simple perfora-

tions. Leaves all radical and arise in two rows

along the rhizome, nearly distichous or nearly

distichous, linear, erect, and more or less trian-

gular in transverse section, not differentiated

into petiole and lamina, parallel-veined, sheath-

ing at the base, and provided with numerous

intravaginal squamules. Stomata mostly para-

cytic. Flowers in scapose, axillary, umbel-like

complex of cymes subtended by (2)3(4) bracts,

bisexual, actinomorphic, 3-merous. Perianth

segments six in two cycles, free, the outer three

a little smaller, greenish and sepal-like, the inner

pink and petaloid. Stamens nine in two cycles,

the outer consisting of three pairs of obliquely

antesepalous members, the inner of three sepa-

rate antepetalous members; ﬁ laments long, erect,

ﬂ attened; anthers basiﬁ xed, tetra-sporangiate,

latrorse. Microsporogenesis successive. Pollen

grains 3-celled, 1-colpate, boat-shaped, tectate-

columellate, reticulate. Gynoecium of 6(-9)

nearly free conduplicate carpels with short sty-

lodia ending in a shortly bilobed and shortly

decurrent stigma; the

margins of each carpel are

never fused but are held together in the distal

portion by interlocking hairs; the basal lateral

sides of the carpels nectariferous (septal

nectaries); each carpel with numerous ovules

scattered over their inner surface, except on the

midrib and edges. Ovules anatropous, bitegmic,

nearly crassinucellate, with parietal cell cut off

from the archesporial cell. Female gametophyte

of Polygonum-type. Endosperm helobial. Fruits

multifollicles. Seeds numerous, small, cylindri-

cal, longitudinally ribbed; seed coat formed by

both integuments, but mainly by testa; embryo

straight, rich of starch; endosperm vestigial, of

thin layer of thick-walled obliterated cells,

n = 8, 10–13. . . . . . . . . . . . . . . 2. butomaceae.

1. APONOGETONACEAE

J. Agardh 1858. 1/50. Tropical and subtropical regions

of the Old World, mostly in Africa and Madagascar.

Aponogeton.

In spite of their highly specialized habit, the

Aponogetonaceae retain such plesiomorphic charac-

ters, as apocarpous gynoecium composed of primitive

carpels with decurrent stigma and 1-colpate pollen

grains.

2. BUTOMACEAE

Mirbel 1804. 1/1. Temperate regions of Eurasia and

North Africa.

Butomus.

Butomus umbellatus, the only member of this

monotypic order, is extremely heterobathmic. In regard

to its apocarpous gynoecium, decurrent stigma, lami-

nar-diffuse placentation, and 1-colpate pollen grains it

is a rather archaic monocot. However, a rather

specialized inﬂ orescence, simple perforations of the

vessels, and very reduced, vestigial endosperm in the

mature seeds makes it a considerably advanced mem-

ber of the monocots.

3. NAJADACEAE

A.L. de Jussieu 1789. 1/40–50. Subcosmopolitan.

Najas.

Closely related and could have originated from the

submerged Hydrocharitaceae (Shaffer-Fehre 1991b;

Haynes et al. 1998), especially to Hydrocharitoideae,

but differ markedly in superior ovary and nuclear

endosperm.

Superorder ALISMATANAE 603

4. HYDROCHARITACEAE

A.L. de Jussieu 1789 (including Blyxaceae Nakai 1949;

Elodeaceae Dumortier 1829; Enhalaceae Nakai 1943;

Halophilaceae J. Agardh 1858; Hydrillaceae Prantl

1879; Stratiotaceae Link 1829; Thalassiaceae Nakai

1943; Vallisneriaceae Link 1829). 17/c.75. Widely dis-

tributed, but mainly in tropics and subtropics.

4.1 HYDROCHARITOIDEAE

Freshwater or rarely marine plants, pollinated at or

above the surface of water. Pollen grains in monads.

Perianth mostly double. – Ottelia, Stratiotes, Hydro-

charis, Limnobium, Blyxa, Apalanthe, Egeria, Elodea,

Hydrilla, Appertiella, Lagarosiphon, Nechamandra,

Maidenia, Vallisneria, Enhalus.

4.2 THALASSIOIDEAE

Marine plants, pollinated beneath the surface of the

water. Pollen grains cohere in moniliform chains; they

form pollen tubes before reaching the stigma. Leaf-

bearing branches arising from the rhizome at distances

of several internodes. Leaves alternate, distichous, with

longitudinal venation. Spathial leaves partly connate.

Inﬂ orescences pedunculate, uniﬂ orous. Flowers dioe-

cious, with three uncolored perianth segments. Stamens

3–13, all fertile; anthers latrorse. Gynoecium of 6–8

carpels; each stylodium divided into two ﬁ liform stig-

mas that are 2–6 times as long as the stylodium; ovary

1-locular or imperfectly 2–3-locular. Fruits with ﬂ eshy

pericarp bursting into a number of irregular, stellately

spreading valves. Seeds conical with a thickened basal

portion. Embryo straight. Cotyledon not coiled. Tannin

cells present. – Thalassia.

4.3 HALOPHILOIDEAE

Marine plants pollinated beneath the water or at the

water surface. Pollen grains cohere in moniliform

chains; they form pollen tube before reaching the

stigma. Leaf-bearing branches arising from the rhizome

at each internode. Leaves opposite, in pseudowhorls or

distichous, sessile or petiolate, linear to ovate, pin-

nately veined. Spathial leaves free. Inﬂ orescences ses-

sile, uniﬂ orous or rarely having one male ﬂ ower and

one female ﬂ ower on one spathe. Flowers monoecious

or dioecious. Male ﬂ owers have three tepals and three

stamens; anthers extrorse. Female ﬂ owers with a vesti-

gial perianth. Gynoecium of 3–5 carpels; stylodia

linear, 3–5, undivided; ovary 1- locular. Fruits ovoid or

globose, with membranous pericarp, dehiscent by

decay of the pericarp. Embryo somewhat curved,

cotyledon spirally coiled upon itself. Tannin cells

absent. – Halophila.

A considerably advanced taxon, which is clearly

closely related to the Butomaceae with which shares a

common origin.

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