Plantago (Plantain, Rib-grass). The foliage-leaves are most frequently scattered, entire, with curved veins, arranged in a rosette close to the ground on an unlimited rhizome; the spike-like inflorescence is borne on a long scape; in some (P. psyllium) the leaves are opposite on a stem with well-developed internodes, and the inflorescences are borne in their axils. The order also presents a transition from insect-pollinated to wind-pollinated flowers. The flowers are protogynous, wind-pollinated in P. major and P. lanceolata, partly also in the other species, but insect pollination also occurs, and P. media has three kinds of flowers, some of which are adapted for wind-pollination (Fig. [571]), others, with short filaments, for insects. Littorella lacustris (Shore-weed) is the most reduced of the Plantaginaceæ: an aquatic plant with rosettes of round, awl-like leaves and diclinous (monœcious) flowers. In the axils of the foliage-leaves is a very short 3-flowered spike, formed by 2 sessile ♀-flowers, and above them a long-stalked ♂-flower; all the flowers are lateral, the terminal one being absent, as in Plantago. The ♂-flower is essentially the same as in Plantago, but the ♀-flower has a scarious corolla, with a narrow, 3–4-dentate mouth, which closes tightly round the nut-like fruit.
Figs. 570, 571.—Plantago media.
Fig. 570.—Diagram of Plantago media.
Fig. 571.—Two different forms of the flower (magnified): 1, chiefly adapted for pollination by wind; 2, for insect-pollination. a The stigma; b the calyx; k the corolla.
The genus Plantago constitutes nearly the entire order (200 species). Some are widely distributed weeds (e.g. P. major, “The white man’s footstep”). In P. psyllium (S. Eur.) the integument of the seeds is mucilaginous, and swells considerably in water.
Family 31. Nuculiferæ.
The flowers are hypogynous and zygomorphic (in Boraginaceæ and Cordiaceæ, however, they are regular, except Echium and Anchusa arvensis). The calyx is gamosepalous, the corolla bilabiate (except in the two orders mentioned), mostly after 2/3, i.e. divided into a 2-leaved posterior portion, and a 3-leaved anterior portion. The æstivation of the corolla is nearly always descending.—In Boraginaceæ and Cordiaceæ there are 5 stamens of equal length; in the other orders 4 didynamous ones, or only 2 fertile; the posterior stamen is sometimes developed as a staminode, sometimes fertile (in Stilbaceæ). The ovary is formed of 2 median carpels (except some Verbenaceæ), with (1-) 2 ovules on each carpel; in the majority of the orders it is, however, divided by a false partition-wall between the dorsal and ventral sutures, into 4 loculi, each of which is often raised independently, causing the style to be situated in the depression between the four lobes (“gynobasic” style, Figs. [572], [573], [575], [579]). The fruit in these orders most frequently becomes a 4-partite schizocarp with nut-like fruitlets. The other orders have a 1(-2)-locular ovary.—The leaves are simple, without stipules.
The family is related to (and proceeds from) the Tubifloræ, especially Convolvulaceæ, which has an almost similar construction of the ovary. It is doubtful whether the Cordiaceæ and Boraginaceæ should be classed with the others.