Haloragaceae

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Haloragaceae

Description

Perennial (rarely annual) herbs, or undershrubs, terrestrial or aquatic, sometimes stoloniferous (Gunnera). Leaves opposite, spiral, or verticillate, in the terrestrial species nearly always simple, in the aquatic ones always partly pinnately divided, pinnately nerved or (in Gunnera) palmately nerved. Stipules 0, but the leaves often flanked by small, subulate and caducous enations. Flowers mostly in spike-like inflorescences, sometimes in a compound panicle, mostly solitary or (sometimes) in clusters of up to a dozen flowers in the axil of a bract or reduced leaf, ☿, monoecious, dioecious or polygamous, perigynous, actinomorphous, mostly 4-merous, or 2-, or (not in Mal.) 3-merous. Sepals 4 or 2, rarely (not in Mal.) 3, in ☿ flowers sometimes much reduced to 0, free or little connate, mostly persistent. Petals alternisepalous, 4, 2 or 0, rarely 3 (not in Mal.), free, in ♀ flowers absent or strongly reduced, often soon caducous, mostly more or less unguiculate and cochleari-form, longer than the sepals. Stamens as many as sepals and then epi- or alternisepalous, or twice as many, 8, 4 or 2, rarely (not in Mal.) 3 fertile and 3 sterile, or 1, in ♀ flowers completely reduced; Ovary 1- or 4-, rarely 2- or (not in Mal.) 3-celled, in the ♂ flowers 0 or reduced; Ovules as many as styles, or (in Gunnera) single, apical, pendulous, anatropous and apotropous. Fruit nut-like or (in Gunnera) a drupe, variously sculptured, indehiscent 1-seeded or breaking up into 4(-2) 1-seeded mericarps. Seed with a thin testa;

Distribution

nearly all over the world: present tropics: present
Genera 7, with c. 150 spp., nearly all over the world, but rather rare in the tropics.

Morphology

Though the enations or trichomes occurring near the leaf-base have been sometimes interpreted as stipules, they are according to SCHINDLER () enatia to which he ascribes a gland function. However this may be, they are also found on the leaves and in other not prescribed places on the stem, showing ihat they are not organs in the proper sense. Recently PRAG-LOWSKY () revised the palynology of the family.

Taxonomy

Haloragaceae are generally agreed to be classified with the Myrtales. The circumscription of the family has differed and has included the genera Callitriche and Hippuris. These are now generally regarded as two separate families, though HUTCHINSON still includes Hippuris (). They were sometimes placed near Haloragaceae, but for example PULLE (Compendium) regarded both as reduced sympetalous families and assumed the reductions to be convergent coinciding with the aquatic habitat, not expressing systematic affinity. This view is sustained by HEGNAUER () and WIEFFERING () on chemotaxonomical arguments. MELCHIOR () and TAKHTAJAN () place only Callitrichaceae near or in Lamiales. HUTCHINSON l.c. places Callitriche in Onagrales.
Within the family Gunnera occupies an isolated position, in which it is mostly regarded as a separate subfamily (SCHINDLER, MELCHIOR); also HUTCHINSON includes it in the family. Others regard it to represent a separate family, placing it next to Haloragaceae, e.g. VON WETTSTEIN, PULLE, and TAKHTAJAN.
The differences between the two groups are the following:

Haloragoideae: Vessels not polystelic. Ligule-like structures absent. Hairs many-celled, rarely reduced few-celled. Bracteoles present, rarely fully absent. Stigma short, capitate or shortly ligulate, on a more or less distinct style. Ovules 2-4, as many as the styles, crassinucellate, with 2 integuments. Fruits without a stone. Endosperm nuclear. Embryo large, cylindrical, with a long radicle.

Subfam. Gunneroideae: Vessels polystelic. Ligule-like structure distinct, sometimes ochrea-like. Hairs one-celled. Bracteoles absent. Stigma long, subulate, sessile. Ovule 1, tenuinucellate, with 1 integument. Fruits with a stone. Endosperm cellular. Embryo small, obcordate, with a short radicle.

However, in general the floral structure is in good agreement to include both in one family. The Australian genus Glischrocaryon (Loudonia) combines characters of both Gunnera and Haloragis, being macromorphologically distinctly allied to Haloragis, but possessing pollen which resembles that of Gunnera (similar type of apertures and exine), thus giving an additional strong argument for keeping Gunneroideae as a subfamily of Haloragaceae.

Subfam. Haloragoideae is divided into tribe Halorageae (with a 1-seeded fruit) and tribe Myrio-phylleae (with the fruit breaking up into 4(-2) 1-seeded mericarps).

Uses

The only useful plant in Malesia is Myriophyllum brasilse /e/iwhich is cultivated in fish-ponds.

Notes

The treatment of Haloragis was done by Mr. N. CASPERS several years ago; while working on Gunnera and Laurembergia, he fell ill and could not finish this work.

Phytochemo

As a consequence of the small economic importance of this family chemical information is scanty. Flavonols, leucoanthocyanins, ellagic acid and rather large amounts of tannins have definitely been demonstrated to be present in members of Haloragaceae. The tannins are most probably mixtures of hydrolysable and condensed tannins; this is indicated by the presence of ellagic acid and leucoanthocyanins. The terms "myriophyllin cells" and "myriophyllin" often used in anatomical literature are derived from Myriophyllum. Myriophyllin cells are idioblasts which are coloured purple by vanillin and hydrochloric acid and myriophyllin is their tannin-like content which gives this reaction (indicating leucoanthocyanins or catechins). Species of Myriophyllum bear trichomes giving the "myriophyllin" test. Two species of Haloragis have been found to produce prussic acid; the cyanogenic compounds, however, have not been investigated. Oxalate of lime occurs frequently, especially in the form of small clusters.
Accumulation of tannins containing ellagic acid and of condensed leucoanthocyanins fits well with the inclusion of Haloragaceae in Myrtales in the wider sense. The genera Callitriche and Hippuris have by some authors been included in or thought affiliated with Haloragaceae, but they are biochemically so different that such a relationship seems highly improbable; their chemical characters rather indicate affinities with sympetalous taxa. Reference: . — R. HEGNAUER.