Perennial plant - Perennial plant

This is a herbaceous plant in which part of the above-ground parts die in winter, but the underground parts hibernate and overwinter, then sprout again from the rhizomes the following spring, grow, and flower (bear fruit). However, there are some above-ground parts that do not die and overwinter with basal leaves (rosette-shaped), and these are collectively called perennial plants. The growing season for perennial plants is mainly from spring to autumn, but there are mountain plants that are weak to the summer heat (heat-tolerant) and tropical plants that are weak to low temperatures (cold-tolerant).

In floriculture, plants are classified as annuals, biennials, perennials, and bulbs based on outdoor cultivation, but these classifications are based on morphology, growth characteristics, seasonal adaptability, etc. and have no relation to botanical taxonomy.

A major feature of perennial plants is that, unlike annual and biennial plants, which are grown by sowing seeds every year, many of them can be planted once and grown without much effort for several years. They are also easy to propagate, and can be propagated vegetatively by division, cuttings (from stems, leaves, and roots), etc., in addition to seeds.

Many perennial plants are native to the Orient, and while many of the flowers native to Japan are perennial plants, there is a geographical distribution in which annual and biennial plants are native to South America and many bulbs are native to the Mediterranean coast. Even in Japan, there are climatic differences between the north and south, and perennial plants can be divided into cold-resistant and heat-resistant. Also, some perennial plants can survive the winter with a little protection from the cold, such as with a frame in winter, and some can withstand the heat if protected with a shade net in summer, so it can be difficult to clearly distinguish between them.

[Yasuo Hori]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

冬には地上部の一部は枯れるが、地下部は休眠状態で越冬し、翌春ふたたび根茎から芽を出し、生育し開花（結実）することを繰り返す草本植物をいう。しかし、一部には地上部も枯死せず根出葉（ロゼット状）の姿で越冬するものもあり、これらを総合して多年草ともよんでいる。宿根草の生育期は主として春から秋にかけてであるが、夏の暑さに弱い（非耐暑性）山草類や、反対に低温に弱い（非耐寒性）熱帯産のものがある。

　花卉(かき)園芸では露地栽培を基準に、一、二年草、宿根草（多年草）、球根類というように区別しているが、これらは形態や生育特性、季節順応性などから区分したもので、植物分類学的な区別とは関係はない。

　宿根草の大きな特色としては、一、二年草のように毎年種子を播(ま)いて育てるのとは異なり、一度植え込んでおくことで数年間手数のかからないものが多い。また繁殖も容易で、種子以外に株分け、挿芽（茎、葉、根の部分）などの栄養繁殖ができる。

　宿根草には東洋原産のものが多く、日本産の草花類の多くは宿根草であるのに対し、一、二年草類は南アメリカ産、球根類の多くは地中海沿岸産というように地理的分布がみられる。日本でも北と南では気候的差があり、耐寒性と耐暑性の宿根草に区分できる。また冬季フレームなどですこしの防寒をすれば越冬できるものや、夏季遮光ネットで保護すれば暑熱を防げる宿根草もあるので、判然とは区別しにくいものもある。

［堀　保男］

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