Plants of Southern California: Agoseris retrorsa, A. grandiflora, and their hybrid

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Table of Contents

Introduction
Distinguishing Characteristics
Geographic Distribution of These Taxa in the Cuyamaca Mountains

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Fig. 1. Young plants of Agoseris retrorsa and A. grandiflora growing together in Cuyamaca Rancho State Park along the Azalea Spring Trail on 28 May 2021. Even these young plants show well the typical difference between these species in their leaf shapes. A. retrorsa has a narrow leaf rachis, with deep lobes that are pointed backward. A. grandiflora has a wider leaf, generally entire or with very shallow lobes, but sometimes with deeper lobes that are not pointed backward; see Fig. 3.

Note that a leaf from an unlabeled A. retrorsa extends through the base of the labeled A. grandiflora.

Click on the picture for a larger version.

Fig. 2. Mature plants of A. retrorsa (left) and A. grandiflora (right). Two extreme forms of A. grandiflora are shown, one with very wide, entire leaves (top right), and one with mostly lobed leaves (bottom right). A. retrorsa has no such extreme variation. The two examples shown look very similar. Click on the pictures for larger versions.

Fig. 3. Closeup of a typical leaf of A. retrorsa (top row); a leaf of the hybrid between A. grandiflora and A. retrorsa (second row); one of the most lobed leaves of A. grandiflora on a very robust plant (third row); and typical leaves of A. grandiflora in a younger plant (bottom row). Click on the pictures for larger versions.

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Fig. 4. Heads of A. grandiflora (left) and A. retrorsa, from plants growing together on the Cold Stream Trail in Cuyamaca Rancho State Park on 24 May 2021. This is both a fair comparison for one point in time, and an unfair comparison because the heads are at different stages in their development.

A. grandiflora matures later than A. retrorsa in the Laguna Mountains. See pix of the two plants, showing that this plant of A. retrorsa is in fruit, whereas the plant of A. grandiflora is still budding.

The heads of A. retrorsa are generally larger than the heads of A. grandiflora at the same stage of bloom and fruit. However, the heads of both species elongate in fruit, so the comparison of the two heads here is not an apple-to-apple comparison since they are not as the same stage of flower/fruit. The Flora of North America gives the involucre of A. grandiflora var. grandiflora as 3 to 5.5 cm in fruit, and the involucre of A. retrorsa as 4 to 6.0 cm in fruit.

Fig. 5. Randomly-selected heads in fruit of A. grandiflora (left) and of A. retrorsa (right) shown at the same scale. Despite the common name of grand mountain dandelion for A. grandiflora, implying a large size, the heads of A. retrorsa are generally larger. Click on the pictures for larger versions.

Fig. 6. Randomly-selected seeds of A. grandiflora (left) and of A. retrorsa (right), shown to the same scale. The seeds of A. grandiflora are fusiform, widest in the middle and tapering on both ends. The seeds of A. retrorsa have a truncate apex, tapering gradually to their base. The body of the A. grandiflora seed on the left is 5.3 mm long. The body of the A. retrorsa seed on the right is 7.0 mm long. Click on the pictures for larger versions.

Introduction

Distinguishing Characteristics

Geographic Distribution of These Taxa in the Cuyamaca Mountains

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• Native and Introduced Plants of Southern California