Rare Plant Program

Numerical Analysis of this and Previous Editions

(from CNPS Inventory, 6th Edition, 2001)

As the following numerical comparison of the plants in the six Inventory editions demonstrates, the size of California's rare and endangered flora continues to grow (Table 1). The percentages given below indicate the portion of the total native flora in California represented by the plants on a particular list for the different editions. We estimate that the flora as currently described contains 6300 native species, subspecies, and varieties. This is the number of native taxa that are fully described in The Jepson Manual (about 6000), plus the approximate number that receive peripheral mention as minor taxa.

Table 1. Numerical comparison of the SIX CNPS Inventory editions. We have reevaluated percent of flora for past editions based on 6300 native plants in California.

There is a net addition of 164 plants (19% increase) to our highest priority list (1B) since the 1994 edition. Over 100 of these have been upgraded to List 1B from a lower priority list, in some cases because we have learned more about their rarity or endangerment, but often because conditions have worsened and they are now more seriously endangered than before. Two sobering facts have emerged during preparation of this edition: over 16% of California's native plants are either exceedingly rare or seriously endangered, and a full one third of our native flora is considered worthy of inclusion in the Inventory. Our best efforts to date simply have not been sufficient to stem the further deterioration of California's rich native flora.

In the last seven years we have identified 351 new rare and endangered plants (Table 2). These new taxa fall into at least five categories: rare plants which have been overlooked in previous editions, plants which are becoming endangered as habitat loss and other threats accelerate, new plants which have been described in California in the last seven years, plants newly "created" by taxonomic changes, and non-vascular plants (28 taxa) which have been added to the Inventory for the first time.

Table 2. Percentage of fifth edition taxa on each list compared to the number and percentage of new sixth edition taxa on each list.

A disproportionate number of the taxa that are new to this Inventory have been assigned to List 2 (Table 2). In the 1994 edition, List 2 represented only 16% of the plants, but this list comprises 38% of the newly added plants in the sixth edition; this follows a trend also noted in the fifth edition. We assume this is primarily due to continued botanical exploration on California's fringes, where most List 2 plants occur, and to the addition of rare bryophytes to this volume, most of which also occur elsewhere in North America. The continued growth of List 2 matches our growing recognition of the importance of protecting plants that, although more common elsewhere, are rare here. By protecting populations that are disjunct or at edge of their range, we make an important contribution to the conservation of genetic diversity and evolutionary processes within species, and help to maintain the resilience species need for survival in the face of rapid environmental change.

California's rare flora is disproportionately rich in subspecies and varieties as compared to the flora as a whole (Table 3). This is unsurprising since subspecies and varieties typically have smaller ranges than species, and are thus biologically rarer to begin with, and consequently more susceptible to disruption. Subspecies and varieties are morphologically, genetically, and geographically distinctive, and much of California's floristic diversity is expressed at this infra-specific level. It is therefore essential that our conservation efforts include these ranks as well as full species if we are to preserve the California flora as the remarkable living evolutionary laboratory that it is.

Table 3. Comparison of taxonomic rank of plants in the California flora, in current and previous editions of the Inventory.