Pentstemon.—The popular garden varieties have sprung from P. Hartwegii and P. Cobaea. Other distinct kinds are P. campanulatus, 1½ ft., pale rose, of bushy habit; P. humilis, 9 in., bright blue; P. speciosus, cyananthus and Jaffrayanus, 2 to 3 ft., all bright blue; P. barbatus, 3 to 4 ft., scarlet, in long terminal panicles; P. Murrayanus, 6 ft., with scarlet flowers and connate leaves; and P. Palmeri, 3 to 4 ft., with large, wide-tubed, rose-coloured flowers.
Petasites.—P. fragrans, the Winter Heliotrope, though of weedy habit, with ample cordate coltsfoot-like leaves, yields in January and February its abundant spikes, about 1 ft. high, of greyish flowers scented like heliotrope; it should have a corner to itself.
Phlomis.—Bold and showy labiates, growing in ordinary soil. P. Russelliana (lunariaefolia), 4 ft., yellow, and P. tuberosa, 3 ft., purplish-rose, both with downy hoary leaves, come in well in broad flower borders.
Phygelius.—P. capensis from South Africa is hardy south of the Thames and in favoured localities. Flowers tubular scarlet, on branching stems, 2 to 3 ft. high. Requires light, rich soil.
Physalis.—P. Alkekengi from South Europe has long been known in gardens for its bright orange-red globular calyxes. It has been surpassed by the much larger and finer P. Francheti from Japan; the brilliant calyxes are often 3 in. in diameter in autumn. Grows in any garden soil.
Physostegia.—Tall, autumn-blooming labiates, of easy growth in ordinary garden soils. P. imbricata, 5 to 6 ft., has pale purple flowers in closely imbricated spikes.
Phytolacca.—Ornamental strong-growing perennials requiring much space. P. acinosa, from the Himalayas, 3 to 4 ft., with whitish flowers in erect spikes. P. decandra, the North American Poke Weed or Red Ink plant, grows 5 to 10 ft. high, has fleshy poisonous roots, erect purple stems and white flowers. P. icosandra, from Mexico, 2 to 3 ft., pinky white. The foliage in all cases is handsome. Ordinary garden soil.
Platycodon.—P. grandiflorum, 6 to 24 in. high, is a fine Chinese perennial with flattish, bell-shaped flowers, 2 to 3 in. across, and purple in colour. The variety Mariesi (or pumilum) is dwarf, with larger, deeper-coloured flowers. Requires rich sandy loam.
Podophyllum.—Ornamental herbs with large lobed leaves. P. Emodi, 6 to 12 in. high, from the Himalayas, has large white or pale-rose flowers, and in autumn bright red, hen’s-egg-like fruits. P. peltatum, the North American mandrake, has large umbrella-like leaves and white flowers; P. pleianthum, from China, purple. They all require moist, peaty soil in warm, sheltered nooks.
Polemonium.—Pretty border flowers. P. coeruleum (Jacob’s Ladder), 2 ft., has elegant pinnate leaves, and long panicles of blue rotate flowers. The variety called variegatum has very elegantly marked leaves, and is sometimes used as a margin or otherwise in bedding arrangements. Good garden soil.